diff --git a/FortranRuntime/test/NonGtestUnit/lit.site.cfg.py.in b/FortranRuntime/test/NonGtestUnit/lit.site.cfg.py.in
deleted file mode 100644
index 3d1780a5d600a9..00000000000000
--- a/FortranRuntime/test/NonGtestUnit/lit.site.cfg.py.in
+++ /dev/null
@@ -1,13 +0,0 @@
-@LIT_SITE_CFG_IN_HEADER@
-
-import os
-
-config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
-config.fortranruntime_binary_dir = "@FORTRANRUNTIME_BINARY_DIR@"
-config.fortranruntime_binary_test_dir = os.path.dirname(__file__)
-
-import lit.llvm
-lit.llvm.initialize(lit_config, config)
-
-# Let the main config do the real work.
-lit_config.load_config(config, "@FORTRANRUNTIME_SOURCE_DIR@/test/NonGtestUnit/lit.cfg.py")
diff --git a/FortranRuntime/test/Unit/lit.site.cfg.py.in b/FortranRuntime/test/Unit/lit.site.cfg.py.in
deleted file mode 100644
index fa993aa897faca..00000000000000
--- a/FortranRuntime/test/Unit/lit.site.cfg.py.in
+++ /dev/null
@@ -1,14 +0,0 @@
-@LIT_SITE_CFG_IN_HEADER@
-
-import os
-
-config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
-config.llvm_build_mode = "@LLVM_BUILD_MODE@"
-config.fortranruntime_binary_dir = "@FORTRANRUNTIME_BINARY_DIR@"
-config.fortranruntime_binary_test_dir = os.path.dirname(__file__)
-
-import lit.llvm
-lit.llvm.initialize(lit_config, config)
-
-# Let the main config do the real work.
-lit_config.load_config(config, "@FORTRANRUNTIME_SOURCE_DIR@/test/Unit/lit.cfg.py")
diff --git a/FortranRuntime/test/lit.site.cfg.py.in b/FortranRuntime/test/lit.site.cfg.py.in
deleted file mode 100644
index a21fc128086eae..00000000000000
--- a/FortranRuntime/test/lit.site.cfg.py.in
+++ /dev/null
@@ -1,18 +0,0 @@
-@LIT_SITE_CFG_IN_HEADER@
-
-import sys
-
-config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
-config.build_lib_dir = "@FORTRANRUNTIME_BUILD_LIB_DIR@"
-config.flang_source_dir = "@FLANG_SOURCE_DIR@"
-config.fortranruntime_source_dir = "@FORTRANRUNTIME_SOURCE_DIR@"
-config.fortranruntime_binary_test_dir = os.path.dirname(__file__)
-config.fortranruntime_build_lib_dir = "@FORTRANRUNTIME_BUILD_LIB_DIR@"
-config.cc = "@CMAKE_C_COMPILER@"
-config.osx_sysroot = path(r"@CMAKE_OSX_SYSROOT@")
-
-import lit.llvm
-lit.llvm.initialize(lit_config, config)
-
-# Let the main config do the real work.
-lit_config.load_config(config, "@FORTRANRUNTIME_SOURCE_DIR@/test/lit.cfg.py")
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 5e4057116a97cb..ed2539cb4e3c5e 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1291,7 +1291,7 @@ void tools::addOpenMPHostOffloadingArgs(const Compilation &C,
 /// Add Fortran runtime libs
 void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
                                   llvm::opt::ArgStringList &CmdArgs) {
-  // Link FortranRuntime
+  // Link flang_rt
   // These are handled earlier on Windows by telling the frontend driver to
   // add the correct libraries to link against as dependents in the object
   // file.
@@ -1307,7 +1307,7 @@ void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
       if (AsNeeded)
         addAsNeededOption(TC, Args, CmdArgs, /*as_needed=*/false);
     }
-    CmdArgs.push_back("-lFortranRuntime");
+    CmdArgs.push_back("-lflang_rt");
   }
 }
 
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index aff656d74daa2f..072d57e8a7ff46 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -304,26 +304,26 @@ static void processVSRuntimeLibrary(const ToolChain &TC, const ArgList &Args,
   case options::OPT__SLASH_MT:
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("--dependent-lib=libcmt");
-    CmdArgs.push_back("--dependent-lib=FortranRuntime.static.lib");
+    CmdArgs.push_back("--dependent-lib=flang_rt.static.lib");
     break;
   case options::OPT__SLASH_MTd:
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("-D_DEBUG");
     CmdArgs.push_back("--dependent-lib=libcmtd");
-    CmdArgs.push_back("--dependent-lib=FortranRuntime.static_dbg.lib");
+    CmdArgs.push_back("--dependent-lib=flang_rt.static_dbg.lib");
     break;
   case options::OPT__SLASH_MD:
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("-D_DLL");
     CmdArgs.push_back("--dependent-lib=msvcrt");
-    CmdArgs.push_back("--dependent-lib=FortranRuntime.dynamic.lib");
+    CmdArgs.push_back("--dependent-lib=flang_rt.dynamic.lib");
     break;
   case options::OPT__SLASH_MDd:
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("-D_DEBUG");
     CmdArgs.push_back("-D_DLL");
     CmdArgs.push_back("--dependent-lib=msvcrtd");
-    CmdArgs.push_back("--dependent-lib=FortranRuntime.dynamic_dbg.lib");
+    CmdArgs.push_back("--dependent-lib=flang_rt.dynamic_dbg.lib");
     break;
   }
 }
diff --git a/FortranRuntime/.clang-format b/flang-rt/.clang-format
similarity index 100%
rename from FortranRuntime/.clang-format
rename to flang-rt/.clang-format
diff --git a/FortranRuntime/.clang-tidy b/flang-rt/.clang-tidy
similarity index 100%
rename from FortranRuntime/.clang-tidy
rename to flang-rt/.clang-tidy
diff --git a/FortranRuntime/CMakeLists.txt b/flang-rt/CMakeLists.txt
similarity index 54%
rename from FortranRuntime/CMakeLists.txt
rename to flang-rt/CMakeLists.txt
index e65cab7060cb02..bd83a51482f4af 100644
--- a/FortranRuntime/CMakeLists.txt
+++ b/flang-rt/CMakeLists.txt
@@ -6,23 +6,23 @@
 #
 #===------------------------------------------------------------------------===#
 #
-# Build instructions for the FortranRuntime library and Fortran modules required
-# by programs compiled by Flang. This is file is intended to be included using
-# the LLVM_ENABLE_RUNTIMES mechanism.
+# Build instructions for the flang-rt library. This is file is intended to be
+# included using the LLVM_ENABLE_RUNTIMES mechanism.
 #
 #===------------------------------------------------------------------------===#
 
 set(LLVM_SUBPROJECT_TITLE "Fortran Runtime")
-set(FORTRANRUNTIME_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
-set(FORTRANRUNTIME_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}")
+set(FLANGRT_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
+set(FLANGRT_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}")
 set(FLANG_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../flang")
 
 enable_language(Fortran)
 
 list(APPEND CMAKE_MODULE_PATH
-  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules"
+    "${FLANGRT_SOURCE_DIR}/cmake/modules"
+    "${FLANG_SOURCE_DIR}/cmake/modules"
   )
-include(AddFortranRuntime)
+include(AddFlangRT)
 include(FlangCommon)
 
 
@@ -30,7 +30,7 @@ include(FlangCommon)
 # Build Mode Introspection #
 ############################
 
-# Setting these variables from an LLVM build is sufficient that FortranRuntime can
+# Setting these variables from an LLVM build is sufficient that flang-rt can
 # construct the output paths, so it can behave as if it were in-tree here.
 set(LLVM_TREE_AVAILABLE OFF)
 if (LLVM_LIBRARY_OUTPUT_INTDIR AND LLVM_RUNTIME_OUTPUT_INTDIR AND PACKAGE_VERSION)
@@ -42,19 +42,19 @@ if (LLVM_TREE_AVAILABLE)
   # Despite Clang in the name, get_clang_resource_dir does not depend on Clang being added to the build
   # flang-new uses the same resource dir as clang.
   include(GetClangResourceDir)
-  get_clang_resource_dir(FORTRANRUNTIME_BUILD_LIB_DIR PREFIX "${LLVM_LIBRARY_OUTPUT_INTDIR}/.." SUBDIR "lib${LLVM_LIBDIR_SUFFIX}")
-  get_clang_resource_dir(FORTRANRUNTIME_INSTALL_LIB_DIR SUBDIR "lib${LLVM_LIBDIR_SUFFIX}") # No prefix, CMake's install command find the install prefix itself
+  get_clang_resource_dir(FLANGRT_BUILD_LIB_DIR PREFIX "${LLVM_LIBRARY_OUTPUT_INTDIR}/.." SUBDIR "lib${LLVM_LIBDIR_SUFFIX}")
+  get_clang_resource_dir(FLANGRT_INSTALL_LIB_DIR SUBDIR "lib${LLVM_LIBDIR_SUFFIX}") # No prefix, CMake's install command find the install prefix itself
 else ()
-  set(FORTRANRUNTIME_BUILD_LIB_DIR "${LLVM_LIBRARY_OUTPUT_INTDIR}")
-  set(FORTRANRUNTIME_INSTALL_LIB_DIR "lib${LLVM_LIBDIR_SUFFIX}")
+  set(FLANGRT_BUILD_LIB_DIR "${LLVM_LIBRARY_OUTPUT_INTDIR}")
+  set(FLANGRT_INSTALL_LIB_DIR "lib${LLVM_LIBDIR_SUFFIX}")
 endif ()
 
 if (DEFINED WIN32)
-  set(FORTRANRUNTIME_BUILD_LIB_DIR "${FORTRANRUNTIME_BUILD_LIB_DIR}/windows")
-  set(FORTRANRUNTIME_INSTALL_LIB_DIR "${FORTRANRUNTIME_INSTALL_LIB_DIR}/windows")
+  set(FLANGRT_BUILD_LIB_DIR "${FLANGRT_BUILD_LIB_DIR}/windows")
+  set(FLANGRT_INSTALL_LIB_DIR "${FLANGRT_INSTALL_LIB_DIR}/windows")
 elseif (LLVM_ENABLE_PER_TARGET_RUNTIME_DIR)
-  set(FORTRANRUNTIME_BUILD_LIB_DIR "${FORTRANRUNTIME_BUILD_LIB_DIR}/${LLVM_TARGET_TRIPLE}")
-  set(FORTRANRUNTIME_INSTALL_LIB_DIR "${FORTRANRUNTIME_INSTALL_LIB_DIR}/${LLVM_TARGET_TRIPLE}")
+  set(FLANGRT_BUILD_LIB_DIR "${FLANGRT_BUILD_LIB_DIR}/${LLVM_TARGET_TRIPLE}")
+  set(FLANGRT_INSTALL_LIB_DIR "${FLANGRT_INSTALL_LIB_DIR}/${LLVM_TARGET_TRIPLE}")
 endif ()
 
 
@@ -62,26 +62,30 @@ endif ()
 # Build Options #
 #################
 
-option(FORTRANRUNTIME_INCLUDE_TESTS "Generate build targets for the FortranRuntime unit and regression-tests." "${LLVM_INCLUDE_TESTS}")
-
-set(FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT "" CACHE STRING "Compile FortranRuntime with GPU support (CUDA or OpenMP)")
-set_property(CACHE FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT PROPERTY STRINGS
-  ""
-  CUDA
-  OpenMP)
-if (NOT FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT)
-elseif (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
-  set(FORTRANRUNTIME_LIBCUDACXX_PATH "" CACHE PATH "Path to libcu++ package installation")
-  option(FORTRANRUNTIME_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS "Do not compile global variables' definitions when producing PTX library" OFF)
-elseif (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
-set(FORTRANRUNTIME_DEVICE_ARCHITECTURES "all" CACHE STRING
+# Important: flang-rt user options must be prefixed with "FLANG_RT_". Variables
+# with this prefix will be forwarded in bootstrap builds.
+
+option(FLANG_RT_INCLUDE_TESTS "Generate build targets for the flang-rt unit and regression-tests." "${LLVM_INCLUDE_TESTS}")
+
+set(FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT "" CACHE STRING "Compile flang-rt with GPU support (CUDA or OpenMP)")
+set_property(CACHE FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT PROPERTY STRINGS
+    ""
+    CUDA
+    OpenMP
+  )
+if (NOT FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT)
+elseif (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
+  set(FLANG_RT_LIBCUDACXX_PATH "" CACHE PATH "Path to libcu++ package installation")
+  option(FLANG_RT_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS "Do not compile global variables' definitions when producing PTX library" OFF)
+elseif (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
+set(FLANG_RT_DEVICE_ARCHITECTURES "all" CACHE STRING
   "List of OpenMP device architectures to be used to compile the Fortran runtime (e.g. 'gfx1103;sm_90')")
 else ()
-  message(FATAL_ERROR "Invalid value '${FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT}' for FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT; must be empty, 'CUDA', or 'OpenMP'")
+  message(FATAL_ERROR "Invalid value '${FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT}' for FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT; must be empty, 'CUDA', or 'OpenMP'")
 endif ()
 
-option(FORTRANRUNTIME_ENABLE_CUF "Compile CUDA Fortran runtime sources" OFF)
-if (FORTRANRUNTIME_ENABLE_CUF)
+option(FLANG_RT_ENABLE_CUF "Compile CUDA Fortran runtime sources" OFF)
+if (FLANG_RT_ENABLE_CUF)
   find_package(CUDAToolkit REQUIRED)
 endif()
 
@@ -113,9 +117,9 @@ if (WIN32)
       ERROR_QUIET
     )
   if (NOT CXX_COMPILER_PRINT_LIBGCC_PATH_FAILURE AND CXX_COMPILER_PRINT_LIBGCC_PATH_RESULT)
-    string(STRIP "${CXX_COMPILER_PRINT_LIBGCC_PATH_RESULT}" FORTRANRUNTIME_LIBCALL)
+    string(STRIP "${CXX_COMPILER_PRINT_LIBGCC_PATH_RESULT}" FLANGRT_LIBCALL)
   else ()
-    set(FORTRANRUNTIME_LIBCALL "")
+    set(FLANGRT_LIBCALL "")
   endif ()
 endif ()
 
@@ -124,9 +128,9 @@ endif ()
 # Build Preparation #
 #####################
 
-if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT AND FORTRANRUNTIME_INCLUDE_TESTS)
+if (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT AND FLANG_RT_INCLUDE_TESTS)
   # If Fortran runtime is built as CUDA library, the linking
-  # of targets that link FortranRuntime must be done
+  # of targets that link flang-rt must be done
   # with CUDA_RESOLVE_DEVICE_SYMBOLS.
   # CUDA language must be enabled for CUDA_RESOLVE_DEVICE_SYMBOLS
   # to take effect.
@@ -134,7 +138,7 @@ if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT AND FORTRANRUNTIME_INCLUDE_TESTS
 endif()
 
 
-# C++17 required for FortranRuntime, user or other runtimes may override this.
+# C++17 is required for flang-rt; user or other runtimes may override this.
 # GTest included later also requires C++17.
 set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
 set(CMAKE_CXX_STANDARD_REQUIRED YES)
@@ -153,9 +157,9 @@ configure_file(cmake/config.h.cmake.in config.h)
 
 add_subdirectory(lib)
 
-if (FORTRANRUNTIME_INCLUDE_TESTS)
+if (FLANG_RT_INCLUDE_TESTS)
   add_subdirectory(unittests)
   add_subdirectory(test)
 else ()
-  add_custom_target(check-FortranRuntime)
+  add_custom_target(check-flang-rt)
 endif()
diff --git a/FortranRuntime/CODE_OWNERS.TXT b/flang-rt/CODE_OWNERS.TXT
similarity index 100%
rename from FortranRuntime/CODE_OWNERS.TXT
rename to flang-rt/CODE_OWNERS.TXT
diff --git a/FortranRuntime/LICENSE.TXT b/flang-rt/LICENSE.TXT
similarity index 100%
rename from FortranRuntime/LICENSE.TXT
rename to flang-rt/LICENSE.TXT
diff --git a/FortranRuntime/README.md b/flang-rt/README.md
similarity index 76%
rename from FortranRuntime/README.md
rename to flang-rt/README.md
index cb578507f8c96e..01836f9d8f714d 100644
--- a/FortranRuntime/README.md
+++ b/flang-rt/README.md
@@ -6,15 +6,15 @@
 
 -->
 
-# Fortran Runtime
+# Fortran Runtime (flang-rt)
 
-Fortran Runtime is the runtime library for code emitted by the Flang compiler
+Flang-rt is the runtime library for code emitted by the Flang compiler
 (https://flang.llvm.org).
 
 
 ## Getting Started
 
-There are two build modes for the FortranRuntime. The bootstrap build, also
+There are two build modes for the flang-rt. The bootstrap build, also
 called the in-tree build, and the runtime-only build, also called the
 out-of-tree build.
 Not to be confused with the terms
@@ -29,29 +29,29 @@ source directory. LLVM does not support in-source builds.
 
 Requirements:
   * [Same as LLVM](https://llvm.org/docs/GettingStarted.html#requirements).
-  * While for LLVM C++14 suffices, Flang and FortranRuntime require a
+  * While for LLVM C++14 suffices, Flang and flang-rt require a
     C++17-capable C++ compiler.
 
 
 ### Bootstrap/In-Tree Build
 
 The bootstrap build will first build Clang and Flang, then use these compilers
-to compile the FortranRuntime. CMake will create a secondary build tree in
+to compile flang-rt. CMake will create a secondary build tree in
 configured with these just-built compilers. The secondary build will reuse the
 same build options (Flags, Debug/Release, ...) as the primary build. It will
-also ensure that once built, the FortranRuntime is found by Flang from either
-the build- or install-prefix. To enable, add `FortranRuntime` to
+also ensure that once built, flang-rt is found by Flang from either
+the build- or install-prefix. To enable, add `flang-rt` to
 `LLVM_ENABLE_RUNTIMES`:
 
 ```bash
 cmake -S <path-to-llvm-project>/llvm    \
   -DNinja                               \
   -DLLVM_ENABLE_PROJECTS=flang          \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
+  -DLLVM_ENABLE_RUNTIMES=flang-rt \
   ...
 ```
 
-It is recommended to enable building OpenMP alongside Flang and FortranRuntime
+It is recommended to enable building OpenMP alongside Flang and flang-rt
 as well. This will build `omp_lib.mod` required to use OpenMP from Fortran.
 Building Compiler-RT may also be required, particularly on platforms that do
 not provide all C-ABI functionality (such as Windows).
@@ -61,7 +61,7 @@ cmake -S <path-to-llvm-project>/llvm                  \
   -DNinja                                             \
   -DCMAKE_BUILD_TYPE=Release                          \
   -DLLVM_ENABLE_PROJECTS="flang;openmp"               \
-  -DLLVM_ENABLE_RUNTIMES="compiler-rt;FortranRuntime" \
+  -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang-rt" \
   ...
 ```
 
@@ -74,8 +74,8 @@ cross-compilation via `flang-new --target=<target-triple>`, add more triples to
 After configuration, build, test, and install the runtime(s) via
 
 ```shell
-$ ninja FortranRuntime
-$ ninja check-FortranRuntime
+$ ninja flang-rt
+$ ninja check-flang-rt
 $ ninja install
 ```
 
@@ -87,7 +87,7 @@ CMake's environment introspection to find a C, C++, and Fortran compiler. The
 compiler to be used can be controlled using CMake's standard mechanisms such as
 `CMAKE_CXX_COMPILER`, `CMAKE_CXX_COMPILER`, and `CMAKE_Fortran_COMPILER`.
 `CMAKE_Fortran_COMPILER` must be `flang-new` built from the same Git commit as
-FortranRuntime to ensure they are using the same ABI. The C and C++ compiler
+flang-rt to ensure they are using the same ABI. The C and C++ compiler
 can be any compiler supporting the same ABI.
 
 In addition to the compiler, the build be able to find LLVM development tools
@@ -100,13 +100,13 @@ cmake -S <path-to-llvm-project>/runtimes                         \
   -GNinja                                                        \
   -DLLVM_BINARY_DIR=<path-to-llvm-builddir>                      \
   -DCMAKE_Fortran_COMPILER=<path-to-llvm-builddir>/bin/flang-new \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime                          \
+  -DLLVM_ENABLE_RUNTIMES=flang-rt                                \
   ...
 ```
 
-Building the FortranRuntime for cross-compilation triple, the target triple can
+Building flang-rt for cross-compilation triple, the target triple can
 be selected using `LLVM_DEFAULT_TARGET_TRIPLE` AND `LLVM_RUNTIMES_TARGET`.
-Of course, FortranRuntime can be built multiple times with different build
+Of course, flang-rt can be built multiple times with different build
 configurations, but have to be located manually when using with the Flang
 driver using the `-L` option.
 
@@ -117,7 +117,7 @@ cmake -S <path-to-llvm-project>/runtimes
   -GNinja                                                                         \
   -DCMAKE_BUILD_TYPE=Release                                                      \
   -DCMAKE_INSTALL_PREFIX="${HOME}/local"                                          \
-  -DLLVM_ENABLE_RUNTIMES="compiler-rt;FortranRuntime"                             \
+  -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang-rt"                                   \
   -DCMAKE_C_COMPILER=gcc                                                          \
   -DCMAKE_CXX_COMPILER=g++                                                        \
   -DLLVM_BINARY_DIR=<path-to-llvm-builddir>                                       \
@@ -131,13 +131,13 @@ cmake -S <path-to-llvm-project>/runtimes
 
 ## Configuration Option Reference
 
-The FortranRuntime has the followign configuration options. This is in
+Flang-rt has the followign configuration options. This is in
 addition to the build options the LLVM_ENABLE_RUNTIMES mechanism and
 CMake itself provide.
 
- * `FORTRANRUNTIME_INCLUDE_TESTS` (boolean; default: `ON`)
+ * `FLANG_RT_INCLUDE_TESTS` (boolean; default: `ON`)
 
-   When `OFF`, does not add any tests and unittests. The `check-FortranRuntime`
+   When `OFF`, does not add any tests and unittests. The `check-flang-rt`
    build target will do nothing.
 
  * `FLANG_RUNTIME_F128_MATH_LIB` (default: `""`)
@@ -148,20 +148,20 @@ CMake itself provide.
    the compiler for `__float128` or 128-bit `long double` support.
    [More details](docs/Real16MathSupport.md).
 
- * `FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT` (values: `"CUDA"`,`"OpenMP"`, `""` default: `""`)
+ * `FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT` (values: `"CUDA"`,`"OpenMP"`, `""` default: `""`)
 
-   When set to `CUDA`, builds a FortranRuntime with experimental support for GPU
+   When set to `CUDA`, builds flang-rt with experimental support for GPU
    accelerators using CUDA. `CMAKE_CUDA_COMPILER` must be set if not
    automatically detected by CMake. `nvcc` as well as `clang` are supported.
 
-   When set to `OpenMP`, builds a FortranRuntime with experimental support for
+   When set to `OpenMP`, builds flang-rt with experimental support for
    GPU accelerators using OpenMP offloading. Only Clang is supported for
    `CMAKE_C_COMPILER` and `CMAKE_CXX_COMPILER`.
 
- * `FORTRANRUNTIME_ENABLE_CUF` (bool, default: `OFF`)
+ * `FLANG_RT_ENABLE_CUF` (bool, default: `OFF`)
 
    Compiles the `libCufRuntime_cuda_<CUDA-version>.a/.so` library. This is
-   independent of `FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA` and only
+   independent of `FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA` and only
    requires a
    [CUDA Toolkit installation](https://cmake.org/cmake/help/latest/module/FindCUDAToolkit.html)
    (no `CMAKE_CUDA_COMPILER`).
@@ -169,14 +169,14 @@ CMake itself provide.
 
 ### CUDA Support
 
-With `-DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA`, the following
+With `-DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA`, the following
 additional configuration options become available.
 
- * `FORTRANRUNTIME_LIBCUDACXX_PATH` (path, default: `""`)
+ * `FLANG_RT_LIBCUDACXX_PATH` (path, default: `""`)
 
    Path to libcu++ package installation.
 
- * `FORTRANRUNTIME_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS` (boolean, default: `OFF`)
+ * `FLANG_RT_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS` (boolean, default: `OFF`)
 
    Do not compile global variables' definitions when producing PTX library.
    Default is `OFF`, meaning global variable definitions are compiled by
@@ -185,11 +185,11 @@ additional configuration options become available.
 
 ### OpenMP Offload Support
 
-With `-DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=OpenMP`, the following
+With `-DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=OpenMP`, the following
 additional configuration options become available.
 
- * `FORTRANRUNTIME_DEVICE_ARCHITECTURES` (default: `"all"`)
+ * `FLANG_RT_DEVICE_ARCHITECTURES` (default: `"all"`)
 
-   A list of device architectures that the FortranRuntime is supporting.
+   A list of device architectures that flang-rt is supporting.
    If `"all"` uses a pre-defined list of architectures. Same purpose as
    `LIBOMPTARGET_DEVICE_ARCHITECTURES` from liboffload.
diff --git a/FortranRuntime/cmake/config.h.cmake.in b/flang-rt/cmake/config.h.cmake.in
similarity index 100%
rename from FortranRuntime/cmake/config.h.cmake.in
rename to flang-rt/cmake/config.h.cmake.in
diff --git a/FortranRuntime/cmake/modules/AddFortranRuntime.cmake b/flang-rt/cmake/modules/AddFlangRT.cmake
similarity index 72%
rename from FortranRuntime/cmake/modules/AddFortranRuntime.cmake
rename to flang-rt/cmake/modules/AddFlangRT.cmake
index e9563c6e3a60b9..797eeddae32142 100644
--- a/FortranRuntime/cmake/modules/AddFortranRuntime.cmake
+++ b/flang-rt/cmake/modules/AddFlangRT.cmake
@@ -1,4 +1,4 @@
-#===-- cmake/modules/AddFortranRuntime.cmake -------------------------------===#
+#===-- cmake/modules/AddFlangRT.cmake -------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
@@ -6,11 +6,11 @@
 #
 #===------------------------------------------------------------------------===#
 
-# Builds a library with common options for FortranRuntime.
+# Builds a library with common options for flang-rt.
 #
 # Usage:
 #
-# add_fortranruntime_library(name sources ...
+# add_flangrt_library(name sources ...
 #   SHARED
 #     Build a dynamic (.so/.dll) library
 #   STATIC
@@ -28,7 +28,7 @@
 #   ADDITIONAL_HEADERS
 #     May specify header files for IDE generators.
 # )
-function (add_fortranruntime_library name)
+function (add_flangrt_library name)
   set(options STATIC SHARED OBJECT INSTALL_WITH_TOOLCHAIN EXCLUDE_FROM_ALL LINK_TO_LLVM)
   set(multiValueArgs ADDITIONAL_HEADERS)
   cmake_parse_arguments(ARG
@@ -76,23 +76,23 @@ function (add_fortranruntime_library name)
       )
   endif ()
 
-  # FortranRuntime's public headers
-  target_include_directories(${name} PRIVATE "${FORTRANRUNTIME_SOURCE_DIR}/include")
+  # Flang-rt's public headers
+  target_include_directories(${name} PRIVATE "${FLANGRT_SOURCE_DIR}/include")
 
   # For ISO_Fortran_binding.h to be found by the runtime itself (Accessed as #include "flang/ISO_Fortran_binding.h")
   # User applications can use #include <ISO_Fortran_binding.h>
   target_include_directories(${name} PRIVATE "${FLANG_SOURCE_DIR}/include")
 
-  # For FortranRuntime's configured config.h to be found
-  target_include_directories(${name} PRIVATE "${FORTRANRUNTIME_BINARY_DIR}")
+  # For flang-rt's configured config.h to be found
+  target_include_directories(${name} PRIVATE "${FLANGRT_BINARY_DIR}")
 
-  # Clang/Flang, targeting the MSVC ABI, including clang-cl, should only depends
-  # on msv(u)crt. LLVM still emits libgcc/compiler-rt functions for 128-bit
-  # integer math (__udivti3, __modti3, __fixsfti, __floattidf, ...) that msvc
-  # does not support. We are injecting a dependency to Compiler-RT where these
-  # are implemented.
-  if (MSVC AND (CMAKE_CXX_COMPILER_ID MATCHES ".*Clang") AND FORTRANRUNTIME_LIBCALL)
-    target_compile_options(${name} PRIVATE "$<$<COMPILE_LANGUAGE:CXX,C>:-Xclang>$<$<COMPILE_LANGUAGE:Fortran>:-Xflang>" "--dependent-lib=${FORTRANRUNTIME_LIBCALL}")
+  # Flang/Clang (including clang-cl) -compiled programs targeting the MSVC ABI
+  # should only depend on msv(u)crt. LLVM still emits libgcc/compiler-rt
+  # functions for 128-bit integer math (__udivti3, __modti3, __fixsfti,
+  # __floattidf, ...) that msvc does not support. We are injecting a dependency
+  # to Compiler-RT where these are implemented.
+  if (MSVC AND (CMAKE_CXX_COMPILER_ID MATCHES ".*Clang") AND FLANGRT_LIBCALL)
+    target_compile_options(${name} PRIVATE "$<$<COMPILE_LANGUAGE:CXX,C>:-Xclang>$<$<COMPILE_LANGUAGE:Fortran>:-Xflang>" "--dependent-lib=${FLANGRT_LIBCALL}")
   endif ()
 
   # Non-GTest unittests depend on LLVMSupport
@@ -112,15 +112,15 @@ function (add_fortranruntime_library name)
   if (ARG_INSTALL_WITH_TOOLCHAIN)
     set_target_properties(${name}
       PROPERTIES
-        LIBRARY_OUTPUT_DIRECTORY "${FORTRANRUNTIME_BUILD_LIB_DIR}"
-        ARCHIVE_OUTPUT_DIRECTORY "${FORTRANRUNTIME_BUILD_LIB_DIR}"
-        RUNTIME_OUTPUT_DIRECTORY "${FORTRANRUNTIME_BUILD_LIB_DIR}"
+        LIBRARY_OUTPUT_DIRECTORY "${FLANGRT_BUILD_LIB_DIR}"
+        ARCHIVE_OUTPUT_DIRECTORY "${FLANGRT_BUILD_LIB_DIR}"
+        RUNTIME_OUTPUT_DIRECTORY "${FLANGRT_BUILD_LIB_DIR}"
       )
 
     install(TARGETS ${name}
-        LIBRARY DESTINATION "${FORTRANRUNTIME_INSTALL_LIB_DIR}"
-        ARCHIVE DESTINATION "${FORTRANRUNTIME_INSTALL_LIB_DIR}"
-        RUNTIME DESTINATION "${FORTRANRUNTIME_INSTALL_LIB_DIR}"
+        LIBRARY DESTINATION "${FLANGRT_INSTALL_LIB_DIR}"
+        ARCHIVE DESTINATION "${FLANGRT_INSTALL_LIB_DIR}"
+        RUNTIME DESTINATION "${FLANGRT_INSTALL_LIB_DIR}"
       )
   endif ()
-endfunction (add_fortranruntime_library)
+endfunction (add_flangrt_library)
diff --git a/FortranRuntime/cmake/modules/AddFortranOffloadRuntime.cmake b/flang-rt/cmake/modules/AddFlangRTOffload.cmake
similarity index 82%
rename from FortranRuntime/cmake/modules/AddFortranOffloadRuntime.cmake
rename to flang-rt/cmake/modules/AddFlangRTOffload.cmake
index d60a26ce0f8a86..a6b94602b0456f 100644
--- a/FortranRuntime/cmake/modules/AddFortranOffloadRuntime.cmake
+++ b/flang-rt/cmake/modules/AddFlangRTOffload.cmake
@@ -7,7 +7,7 @@
 #===------------------------------------------------------------------------===#
 
 macro(enable_cuda_compilation name files)
-  if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
+  if (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
     if (BUILD_SHARED_LIBS)
       message(FATAL_ERROR
         "BUILD_SHARED_LIBS is not supported for CUDA build of Fortran runtime"
@@ -42,26 +42,26 @@ macro(enable_cuda_compilation name files)
       "${CUDA_COMPILE_OPTIONS}"
       )
 
-    if (EXISTS "${FORTRANRUNTIME_LIBCUDACXX_PATH}/include")
+    if (EXISTS "${FLANG_RT_LIBCUDACXX_PATH}/include")
       # When using libcudacxx headers files, we have to use them
       # for all files of F18 runtime.
-      include_directories(AFTER ${FORTRANRUNTIME_LIBCUDACXX_PATH}/include)
+      include_directories(AFTER ${FLANG_RT_LIBCUDACXX_PATH}/include)
       add_compile_definitions(RT_USE_LIBCUDACXX=1)
     endif()
 
     # Add an OBJECT library consisting of CUDA PTX.
-    add_fortranruntime_library(${name}PTX OBJECT ${files})
+    add_flangrt_library(${name}PTX OBJECT ${files})
     set_property(TARGET ${name}PTX PROPERTY CUDA_PTX_COMPILATION ON)
-    if (FORTRANRUNTIME_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS)
+    if (FLANG_RT_CUDA_RUNTIME_PTX_WITHOUT_GLOBAL_VARS)
       target_compile_definitions(${name}PTX
-        PRIVATE FORTRANRUNTIME_NO_GLOBAL_VAR_DEFS
+        PRIVATE FLANGRT_NO_GLOBAL_VAR_DEFS
         )
     endif()
   endif()
 endmacro()
 
 macro(enable_omp_offload_compilation files)
-  if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
+  if (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
     # OpenMP offload build only works with Clang compiler currently.
 
     if (BUILD_SHARED_LIBS)
@@ -88,13 +88,13 @@ macro(enable_omp_offload_compilation files)
         "${all_amdgpu_architectures};${all_nvptx_architectures}"
         )
       # TODO: support auto detection on the build system.
-      if (FORTRANRUNTIME_DEVICE_ARCHITECTURES STREQUAL "all")
-        set(FORTRANRUNTIME_DEVICE_ARCHITECTURES ${all_gpu_architectures})
+      if (FLANG_RT_DEVICE_ARCHITECTURES STREQUAL "all")
+        set(FLANG_RT_DEVICE_ARCHITECTURES ${all_gpu_architectures})
       endif()
-      list(REMOVE_DUPLICATES FORTRANRUNTIME_DEVICE_ARCHITECTURES)
+      list(REMOVE_DUPLICATES FLANG_RT_DEVICE_ARCHITECTURES)
 
       string(REPLACE ";" "," compile_for_architectures
-        "${FORTRANRUNTIME_DEVICE_ARCHITECTURES}"
+        "${FLANG_RT_DEVICE_ARCHITECTURES}"
         )
 
       set(OMP_COMPILE_OPTIONS
@@ -115,7 +115,7 @@ macro(enable_omp_offload_compilation files)
         )
     else()
       message(FATAL_ERROR
-        "FortranRuntime build with OpenMP offload is not supported for these compilers:\n"
+        "Flang-rt build with OpenMP offload is not supported for these compilers:\n"
         "CMAKE_CXX_COMPILER_ID: ${CMAKE_CXX_COMPILER_ID}\n"
         "CMAKE_C_COMPILER_ID: ${CMAKE_C_COMPILER_ID}")
     endif()
diff --git a/flang/include/flang/Runtime/CUDA/allocator.h b/flang-rt/include/flang-rt/CufRuntime/allocator.h
similarity index 85%
rename from flang/include/flang/Runtime/CUDA/allocator.h
rename to flang-rt/include/flang-rt/CufRuntime/allocator.h
index cc88896b1f0bd6..63406e0de6d2fa 100644
--- a/flang/include/flang/Runtime/CUDA/allocator.h
+++ b/flang-rt/include/flang-rt/CufRuntime/allocator.h
@@ -1,4 +1,4 @@
-//===-- include/flang/Runtime/CUDA/allocator.h ------------------*- C++ -*-===//
+//===-- include/flang-rt/CufRuntime/allocator.h -----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_CUDA_ALLOCATOR_H_
-#define FORTRAN_RUNTIME_CUDA_ALLOCATOR_H_
+#ifndef FORTRAN_CUFRUNTIME_ALLOCATOR_H_
+#define FORTRAN_CUFRUNTIME_ALLOCATOR_H_
 
 #include "flang/Runtime/descriptor-consts.h"
 #include "flang/Runtime/entry-names.h"
@@ -43,4 +43,4 @@ void *CUFAllocUnified(std::size_t);
 void CUFFreeUnified(void *);
 
 } // namespace Fortran::runtime::cuda
-#endif // FORTRAN_RUNTIME_CUDA_ALLOCATOR_H_
+#endif /* FORTRAN_CUFRUNTIME_ALLOCATOR_H_ */
diff --git a/FortranRuntime/include/FortranRuntime/Runtime/allocator-registry.h b/flang-rt/include/flang-rt/flang_rt/allocator-registry.h
similarity index 87%
rename from FortranRuntime/include/FortranRuntime/Runtime/allocator-registry.h
rename to flang-rt/include/flang-rt/flang_rt/allocator-registry.h
index 30a583b88c083e..ecad61ab4043d7 100644
--- a/FortranRuntime/include/FortranRuntime/Runtime/allocator-registry.h
+++ b/flang-rt/include/flang-rt/flang_rt/allocator-registry.h
@@ -1,4 +1,4 @@
-//===-- include/FortranRuntime/Runtime/allocator-registry.h -----*- C++ -*-===//
+//===-- include/flang-rt/flang_rt/allocator-registry.h ----------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_ALLOCATOR_REGISTRY_H_
-#define FORTRAN_RUNTIME_ALLOCATOR_REGISTRY_H_
+#ifndef FORTRAN_FLANG_RT_ALLOCATOR_REGISTRY_H_
+#define FORTRAN_FLANG_RT_ALLOCATOR_REGISTRY_H_
 
 #include "flang/Common/api-attrs.h"
 #include "flang/Runtime/allocator-registry-consts.h"
@@ -55,4 +55,4 @@ RT_OFFLOAD_VAR_GROUP_END
 
 } // namespace Fortran::runtime
 
-#endif /* FORTRAN_RUNTIME_ALLOCATOR_REGISTRY_H_ */
+#endif /* FORTRAN_FLANG_RT_ALLOCATOR_REGISTRY_H_ */
diff --git a/FortranRuntime/include/FortranRuntime/Runtime/array-constructor.h b/flang-rt/include/flang-rt/flang_rt/array-constructor.h
similarity index 85%
rename from FortranRuntime/include/FortranRuntime/Runtime/array-constructor.h
rename to flang-rt/include/flang-rt/flang_rt/array-constructor.h
index 314d5e56599cd3..e8fffc762b6fbe 100644
--- a/FortranRuntime/include/FortranRuntime/Runtime/array-constructor.h
+++ b/flang-rt/include/flang-rt/flang_rt/array-constructor.h
@@ -1,4 +1,4 @@
-//===-- include/FortranRuntime/Runtime/array-constructor.h ------*- C++ -*-===//
+//===-- include/flang-rt/flang_rt/array-constructor.h -----------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,10 +9,10 @@
 // External APIs to create temporary storage for array constructors when their
 // final extents or length parameters cannot be pre-computed.
 
-#ifndef FORTRAN_RUNTIME_ARRAY_CONSTRUCTOR_H_
-#define FORTRAN_RUNTIME_ARRAY_CONSTRUCTOR_H_
+#ifndef FORTRAN_FLANG_RT_ARRAY_CONSTRUCTOR_H_
+#define FORTRAN_FLANG_RT_ARRAY_CONSTRUCTOR_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "flang/Runtime/array-constructor-consts.h"
 #include "flang/Runtime/entry-names.h"
 #include <cstdint>
@@ -45,4 +45,4 @@ struct ArrayConstructorVector {
 };
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_ARRAY_CONSTRUCTOR_H_ */
+#endif /* FORTRAN_FLANG_RT_ARRAY_CONSTRUCTOR_H_ */
diff --git a/FortranRuntime/include/FortranRuntime/Runtime/descriptor.h b/flang-rt/include/flang-rt/flang_rt/descriptor.h
similarity index 98%
rename from FortranRuntime/include/FortranRuntime/Runtime/descriptor.h
rename to flang-rt/include/flang-rt/flang_rt/descriptor.h
index f79ad6b9637a4a..fea5b55c1922ce 100644
--- a/FortranRuntime/include/FortranRuntime/Runtime/descriptor.h
+++ b/flang-rt/include/flang-rt/flang_rt/descriptor.h
@@ -1,4 +1,4 @@
-//===-- include/FortranRuntime/Runtime/descriptor.h -------------*- C++ -*-===//
+//===-- include/flang-rt/flang_rt/descriptor.h ------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_DESCRIPTOR_H_
-#define FORTRAN_RUNTIME_DESCRIPTOR_H_
+#ifndef FORTRAN_FLANG_RT_DESCRIPTOR_H_
+#define FORTRAN_FLANG_RT_DESCRIPTOR_H_
 
 // Defines data structures used during execution of a Fortran program
 // to implement nontrivial dummy arguments, pointers, allocatables,
@@ -18,8 +18,8 @@
 // User C code is welcome to depend on that ISO_Fortran_binding.h file,
 // but should never reference this internal header.
 
-#include "FortranRuntime/Runtime/memory.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/memory.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Runtime/descriptor-consts.h"
 #include <algorithm>
@@ -482,4 +482,4 @@ class alignas(Descriptor) StaticDescriptor {
 };
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_DESCRIPTOR_H_ */
+#endif /* FORTRAN_FLANG_RT_DESCRIPTOR_H_ */
diff --git a/FortranRuntime/include/FortranRuntime/Runtime/io-api-funcs.h b/flang-rt/include/flang-rt/flang_rt/io-api-funcs.h
similarity index 84%
rename from FortranRuntime/include/FortranRuntime/Runtime/io-api-funcs.h
rename to flang-rt/include/flang-rt/flang_rt/io-api-funcs.h
index 516fe25784656c..00cb49ad015437 100644
--- a/FortranRuntime/include/FortranRuntime/Runtime/io-api-funcs.h
+++ b/flang-rt/include/flang-rt/flang_rt/io-api-funcs.h
@@ -1,4 +1,4 @@
-//===-- include/FortranRuntime/Runtime/io-api-funcs.h -----------*- C++ -*-===//
+//===-- include/flang-rt/flang_rt/io-api-funcs.h ----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Defines API between compiled code and I/O runtime library.
 
-#ifndef FORTRAN_RUNTIME_IO_API_FUNCS_H_
-#define FORTRAN_RUNTIME_IO_API_FUNCS_H_
+#ifndef FORTRAN_FLANG_RT_IO_API_FUNCS_H_
+#define FORTRAN_FLANG_RT_IO_API_FUNCS_H_
 
 #include "flang/Common/uint128.h"
 #include "flang/Runtime/entry-names.h"
@@ -36,4 +36,4 @@ RT_API_ATTRS const char *InquiryKeywordHashDecode(
     char *buffer, std::size_t, InquiryKeywordHash);
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_IO_API_FUNCS_H_ */
+#endif /* FORTRAN_FLANG_RT_IO_API_FUNCS_H_ */
diff --git a/FortranRuntime/include/FortranRuntime/Runtime/iostat-funcs.h b/flang-rt/include/flang-rt/flang_rt/iostat-funcs.h
similarity index 75%
rename from FortranRuntime/include/FortranRuntime/Runtime/iostat-funcs.h
rename to flang-rt/include/flang-rt/flang_rt/iostat-funcs.h
index 10906afb01673c..dd24d41fbaad10 100644
--- a/FortranRuntime/include/FortranRuntime/Runtime/iostat-funcs.h
+++ b/flang-rt/include/flang-rt/flang_rt/iostat-funcs.h
@@ -1,4 +1,4 @@
-//===-- include/FortranRuntime/Runtime/iostat-funcs.h -----------*- C++ -*-===//
+//===-- include/flang-rt/flang_rt/iostat-funcs.h ----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,8 +9,8 @@
 // Defines the values returned by the runtime for IOSTAT= specifiers
 // on I/O statements.
 
-#ifndef FORTRAN_RUNTIME_IOSTAT_FUNCS_H_
-#define FORTRAN_RUNTIME_IOSTAT_FUNCS_H_
+#ifndef FORTRAN_FLANG_RT_IOSTAT_FUNCS_H_
+#define FORTRAN_FLANG_RT_IOSTAT_FUNCS_H_
 
 #include "flang/Common/api-attrs.h"
 #include "flang/Runtime/iostat.h"
@@ -20,4 +20,4 @@ namespace Fortran::runtime::io {
 RT_API_ATTRS const char *IostatErrorString(int);
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_IOSTAT_FUNCS_H_ */
+#endif /* FORTRAN_FLANG_RT_IOSTAT_FUNCS_H_ */
diff --git a/FortranRuntime/include/FortranRuntime/Runtime/memory.h b/flang-rt/include/flang-rt/flang_rt/memory.h
similarity index 96%
rename from FortranRuntime/include/FortranRuntime/Runtime/memory.h
rename to flang-rt/include/flang-rt/flang_rt/memory.h
index 3e7fd2d9ea3e3b..b97f6525d60036 100644
--- a/FortranRuntime/include/FortranRuntime/Runtime/memory.h
+++ b/flang-rt/include/flang-rt/flang_rt/memory.h
@@ -1,4 +1,4 @@
-//===-- include/FortranRuntime/Runtime/memory.h -----------------*- C++ -*-===//
+//===-- include/flang-rt/flang_rt/memory.h ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,8 +9,8 @@
 // Thin wrapper around malloc()/free() to isolate the dependency,
 // ease porting, and provide an owning pointer.
 
-#ifndef FORTRAN_RUNTIME_MEMORY_H_
-#define FORTRAN_RUNTIME_MEMORY_H_
+#ifndef FORTRAN_FLANG_RT_MEMORY_H_
+#define FORTRAN_FLANG_RT_MEMORY_H_
 
 #include "flang/Common/api-attrs.h"
 #include <cassert>
@@ -170,4 +170,4 @@ template <typename A> struct Allocator {
 };
 } // namespace Fortran::runtime
 
-#endif /* FORTRAN_RUNTIME_MEMORY_H_ */
+#endif /* FORTRAN_FLANG_RT_MEMORY_H_ */
diff --git a/FortranRuntime/include/FortranRuntime/Runtime/type-code.h b/flang-rt/include/flang-rt/flang_rt/type-code.h
similarity index 93%
rename from FortranRuntime/include/FortranRuntime/Runtime/type-code.h
rename to flang-rt/include/flang-rt/flang_rt/type-code.h
index 92ff593410c12c..7c694a13431b13 100644
--- a/FortranRuntime/include/FortranRuntime/Runtime/type-code.h
+++ b/flang-rt/include/flang-rt/flang_rt/type-code.h
@@ -1,4 +1,4 @@
-//===-- include/FortranRuntime/Runtime/type-code.h --------------*- C++ -*-===//
+//===-- include/flang-rt/flang_rt/type-code.h -------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_TYPE_CODE_H_
-#define FORTRAN_RUNTIME_TYPE_CODE_H_
+#ifndef FORTRAN_FLANG_RT_TYPE_CODE_H_
+#define FORTRAN_FLANG_RT_TYPE_CODE_H_
 
 #include "flang/Common/Fortran-consts.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
@@ -75,4 +75,4 @@ class TypeCode {
   ISO::CFI_type_t raw_{CFI_type_other};
 };
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_TYPE_CODE_H_ */
+#endif /* FORTRAN_FLANG_RT_TYPE_CODE_H_ */
diff --git a/FortranRuntime/lib/CMakeLists.txt b/flang-rt/lib/CMakeLists.txt
similarity index 71%
rename from FortranRuntime/lib/CMakeLists.txt
rename to flang-rt/lib/CMakeLists.txt
index 74c78b3fa3a493..f0422f5e0a58b4 100644
--- a/FortranRuntime/lib/CMakeLists.txt
+++ b/flang-rt/lib/CMakeLists.txt
@@ -6,8 +6,12 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_subdirectory(Runtime)
-if (FORTRANRUNTIME_INCLUDE_TESTS)
+add_subdirectory(FortranFloat128Math)
+add_subdirectory(flang_rt)
+if (FLANG_RT_ENABLE_CUF)
+  add_subdirectory(CufRuntime)
+endif()
+
+if (FLANG_RT_INCLUDE_TESTS)
   add_subdirectory(Testing)
 endif ()
-
diff --git a/FortranRuntime/lib/Runtime/CUDA/CMakeLists.txt b/flang-rt/lib/CufRuntime/CMakeLists.txt
similarity index 87%
rename from FortranRuntime/lib/Runtime/CUDA/CMakeLists.txt
rename to flang-rt/lib/CufRuntime/CMakeLists.txt
index 78b98652d60813..1eb80d9ca1d497 100644
--- a/FortranRuntime/lib/Runtime/CUDA/CMakeLists.txt
+++ b/flang-rt/lib/CufRuntime/CMakeLists.txt
@@ -1,4 +1,4 @@
-#===-- lib/Runtime/CUDA/CMakeLists.txt -------------------------------------===#
+#===-- lib/CufRuntime/CMakeLists.txt ---------------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
@@ -11,7 +11,7 @@
 # added to the library name.
 set(CUFRT_LIBNAME CufRuntime_cuda_${CUDAToolkit_VERSION_MAJOR})
 
-add_fortranruntime_library(${CUFRT_LIBNAME}
+add_flangrt_library(${CUFRT_LIBNAME}
   allocator.cpp
   descriptor.cpp
 )
@@ -25,6 +25,6 @@ endif()
 
 target_link_libraries(${CUFRT_LIBNAME}
   PRIVATE
-  FortranRuntime
+  flang_rt
   ${CUDA_RT_TARGET}
 )
diff --git a/FortranRuntime/lib/Runtime/CUDA/allocator.cpp b/flang-rt/lib/CufRuntime/allocator.cpp
similarity index 81%
rename from FortranRuntime/lib/Runtime/CUDA/allocator.cpp
rename to flang-rt/lib/CufRuntime/allocator.cpp
index c9d62f6ea8f3bf..8c16fb77f2ac46 100644
--- a/FortranRuntime/lib/Runtime/CUDA/allocator.cpp
+++ b/flang-rt/lib/CufRuntime/allocator.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/CUDA/allocator.cpp --------------------------*- C++ -*-===//
+//===-- lib/CufRuntime/allocator.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,14 +6,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/CUDA/allocator.h"
-#include "FortranRuntime/Runtime/allocator-registry.h"
-#include "../derived.h"
-#include "../stat.h"
-#include "../terminator.h"
-#include "../type-info.h"
-#include "flang/ISO_Fortran_binding_wrapper.h"
-#include "flang/Support/Fortran.h"
+#include "flang-rt/CufRuntime/allocator.h"
+#include "flang-rt/flang_rt/allocator-registry.h"
+#include "../flang_rt/derived.h"
+#include "../flang_rt/stat.h"
+#include "../flang_rt/terminator.h"
+#include "../flang_rt/type-info.h"
+#include "flang/Common/Fortran-consts.h"
+#include "flang/Common/ISO_Fortran_binding_wrapper.h"
 
 #include "cuda_runtime.h"
 
diff --git a/FortranRuntime/lib/Runtime/CUDA/descriptor.cpp b/flang-rt/lib/CufRuntime/descriptor.cpp
similarity index 82%
rename from FortranRuntime/lib/Runtime/CUDA/descriptor.cpp
rename to flang-rt/lib/CufRuntime/descriptor.cpp
index 94b5feca4ce4dc..b034fc76b67d4d 100644
--- a/FortranRuntime/lib/Runtime/CUDA/descriptor.cpp
+++ b/flang-rt/lib/CufRuntime/descriptor.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/CUDA/descriptor.cpp -------------------------*- C++ -*-===//
+//===-- lib/CufRuntime/descriptor.cpp ---------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/CUDA/descriptor.h"
-#include "FortranRuntime/Runtime/CUDA/allocator.h"
+#include "flang/Runtime/CUDA/descriptor.h"
+#include "flang-rt/CufRuntime/allocator.h"
 
 namespace Fortran::runtime::cuda {
 extern "C" {
diff --git a/FortranRuntime/lib/Runtime/Float128Math/CMakeLists.txt b/flang-rt/lib/FortranFloat128Math/CMakeLists.txt
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/CMakeLists.txt
rename to flang-rt/lib/FortranFloat128Math/CMakeLists.txt
index ed65da0a5ac71c..b12dfee64af8f6 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/CMakeLists.txt
+++ b/flang-rt/lib/FortranFloat128Math/CMakeLists.txt
@@ -1,4 +1,4 @@
-#===-- runtime/Float128Math/CMakeLists.txt ---------------------------------===#
+#===-- lib/FortranFloat128Math/CMakeLists.txt ------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
@@ -91,12 +91,11 @@ if (FLANG_RUNTIME_F128_MATH_LIB)
 
   if (WIN32)
     # Do not create a FortranFloat128Math library under Windows, the Flang
-    # driver never links it. Instead, add the sources to the main
-    # FortranRuntime.lib.
+    # driver never links it. Instead, add the sources to the flang_rt itself.
     target_sources(FortranFloat128MathILib INTERFACE ${sources})
     target_compile_definitions(FortranFloat128MathILib INTERFACE HAS_QUADMATHLIB)
   else ()
-    add_fortranruntime_library(FortranFloat128Math STATIC INSTALL_WITH_TOOLCHAIN
+    add_flangrt_library(FortranFloat128Math STATIC INSTALL_WITH_TOOLCHAIN
       ${sources})
    endif ()
 elseif (HAVE_LDBL_MANT_DIG_113)
@@ -108,7 +107,7 @@ elseif (HAVE_LDBL_MANT_DIG_113)
       )
     target_sources(FortranFloat128MathILib INTERFACE ${sources})
   else()
-    message(FATAL_ERROR "FortranRuntime cannot build without libm")
+    message(FATAL_ERROR "flang-rt cannot build without libm")
   endif()
 else()
   # We can use '__float128' version from libc, if it has them.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/acos.cpp b/flang-rt/lib/FortranFloat128Math/acos.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/acos.cpp
rename to flang-rt/lib/FortranFloat128Math/acos.cpp
index 7b15e4a0bfd3ae..e204c6c871f3fa 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/acos.cpp
+++ b/flang-rt/lib/FortranFloat128Math/acos.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/acos.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/acos.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/acosh.cpp b/flang-rt/lib/FortranFloat128Math/acosh.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/acosh.cpp
rename to flang-rt/lib/FortranFloat128Math/acosh.cpp
index c873259b4545b8..90ff7886e6909d 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/acosh.cpp
+++ b/flang-rt/lib/FortranFloat128Math/acosh.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/acosh.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/acosh.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/asin.cpp b/flang-rt/lib/FortranFloat128Math/asin.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/asin.cpp
rename to flang-rt/lib/FortranFloat128Math/asin.cpp
index 8866d51430197a..18368044d72b0f 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/asin.cpp
+++ b/flang-rt/lib/FortranFloat128Math/asin.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/asin.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/asin.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/asinh.cpp b/flang-rt/lib/FortranFloat128Math/asinh.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/asinh.cpp
rename to flang-rt/lib/FortranFloat128Math/asinh.cpp
index 288193001ce1da..2c1f040cfc3872 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/asinh.cpp
+++ b/flang-rt/lib/FortranFloat128Math/asinh.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/asinh.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/asinh.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/atan.cpp b/flang-rt/lib/FortranFloat128Math/atan.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/atan.cpp
rename to flang-rt/lib/FortranFloat128Math/atan.cpp
index 390c080b4d501b..8bd9a2626caf83 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/atan.cpp
+++ b/flang-rt/lib/FortranFloat128Math/atan.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/atan.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/atan.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/atan2.cpp b/flang-rt/lib/FortranFloat128Math/atan2.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/atan2.cpp
rename to flang-rt/lib/FortranFloat128Math/atan2.cpp
index 3c206b75704431..4994be699a0b67 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/atan2.cpp
+++ b/flang-rt/lib/FortranFloat128Math/atan2.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/atan2.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/atan2.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/atanh.cpp b/flang-rt/lib/FortranFloat128Math/atanh.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/atanh.cpp
rename to flang-rt/lib/FortranFloat128Math/atanh.cpp
index 77ceb188f04e42..f5ace35ac51caa 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/atanh.cpp
+++ b/flang-rt/lib/FortranFloat128Math/atanh.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/atanh.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/atanh.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/ceil.cpp b/flang-rt/lib/FortranFloat128Math/ceil.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/ceil.cpp
rename to flang-rt/lib/FortranFloat128Math/ceil.cpp
index 46bc253bd0922d..834da9396c071d 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/ceil.cpp
+++ b/flang-rt/lib/FortranFloat128Math/ceil.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/ceil.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/ceil.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/complex-math.c b/flang-rt/lib/FortranFloat128Math/complex-math.c
similarity index 96%
rename from FortranRuntime/lib/Runtime/Float128Math/complex-math.c
rename to flang-rt/lib/FortranFloat128Math/complex-math.c
index f34ef7da76e599..493ffe942f7e31 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/complex-math.c
+++ b/flang-rt/lib/FortranFloat128Math/complex-math.c
@@ -1,4 +1,4 @@
-/*===-- lib/Runtime/Float128Math/complex-math.c ---------------------*- C -*-===
+/*===-- lib/FortranFloat128Math/complex-math.c ----------------------*- C -*-===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/complex-math.h b/flang-rt/lib/FortranFloat128Math/complex-math.h
similarity index 88%
rename from FortranRuntime/lib/Runtime/Float128Math/complex-math.h
rename to flang-rt/lib/FortranFloat128Math/complex-math.h
index 6f5c7954bab035..bb67523e1bddcc 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/complex-math.h
+++ b/flang-rt/lib/FortranFloat128Math/complex-math.h
@@ -1,4 +1,4 @@
-/*===-- lib/Runtime/Float128Math/complex-math.h ---------------------*- C -*-===
+/*===-- lib/FortranFloat128Math/complex-math.h ----------------------*- C -*-===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
  *
  *===----------------------------------------------------------------------===*/
 
-#ifndef FORTRAN_RUNTIME_FLOAT128MATH_COMPLEX_MATH_H_
-#define FORTRAN_RUNTIME_FLOAT128MATH_COMPLEX_MATH_H_
+#ifndef FORTRAN_FORTRANFLOAT128MATH_COMPLEX_MATH_H_
+#define FORTRAN_FORTRANFLOAT128MATH_COMPLEX_MATH_H_
 
 #include "flang/Common/float128.h"
 #include "flang/Runtime/entry-names.h"
@@ -59,4 +59,4 @@
 #error "Float128Math build with glibc>=2.26 is unsupported yet"
 #endif
 
-#endif /* FORTRAN_RUNTIME_FLOAT128MATH_COMPLEX_MATH_H_ */
+#endif /* FORTRAN_FORTRANFLOAT128MATH_COMPLEX_MATH_H_ */
diff --git a/FortranRuntime/lib/Runtime/Float128Math/cos.cpp b/flang-rt/lib/FortranFloat128Math/cos.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/cos.cpp
rename to flang-rt/lib/FortranFloat128Math/cos.cpp
index 8ce47151e2914b..2651982666118b 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/cos.cpp
+++ b/flang-rt/lib/FortranFloat128Math/cos.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/cos.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/cos.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/cosh.cpp b/flang-rt/lib/FortranFloat128Math/cosh.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/cosh.cpp
rename to flang-rt/lib/FortranFloat128Math/cosh.cpp
index f1ec45bcfb479d..dda01e5abef66d 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/cosh.cpp
+++ b/flang-rt/lib/FortranFloat128Math/cosh.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/cosh.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/cosh.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/erf.cpp b/flang-rt/lib/FortranFloat128Math/erf.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/erf.cpp
rename to flang-rt/lib/FortranFloat128Math/erf.cpp
index 010088467794d1..f5e713d93cac61 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/erf.cpp
+++ b/flang-rt/lib/FortranFloat128Math/erf.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/erf.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/erf.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/erfc.cpp b/flang-rt/lib/FortranFloat128Math/erfc.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/erfc.cpp
rename to flang-rt/lib/FortranFloat128Math/erfc.cpp
index b226f8d2dc378b..3f8b78ba0e64f9 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/erfc.cpp
+++ b/flang-rt/lib/FortranFloat128Math/erfc.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/erfc.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/erfc.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/exp.cpp b/flang-rt/lib/FortranFloat128Math/exp.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/exp.cpp
rename to flang-rt/lib/FortranFloat128Math/exp.cpp
index e22f9df3579e96..0b694b159f3621 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/exp.cpp
+++ b/flang-rt/lib/FortranFloat128Math/exp.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/exp.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/exp.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/exponent.cpp b/flang-rt/lib/FortranFloat128Math/exponent.cpp
similarity index 92%
rename from FortranRuntime/lib/Runtime/Float128Math/exponent.cpp
rename to flang-rt/lib/FortranFloat128Math/exponent.cpp
index f07bf30bd1096f..a9c1b867e7ea37 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/exponent.cpp
+++ b/flang-rt/lib/FortranFloat128Math/exponent.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/exponent.cpp -------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/exponent.cpp --------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/floor.cpp b/flang-rt/lib/FortranFloat128Math/floor.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/floor.cpp
rename to flang-rt/lib/FortranFloat128Math/floor.cpp
index 8744e6e2fec63c..27cfed2f1f9599 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/floor.cpp
+++ b/flang-rt/lib/FortranFloat128Math/floor.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/floor.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/floor.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/fma.cpp b/flang-rt/lib/FortranFloat128Math/fma.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/fma.cpp
rename to flang-rt/lib/FortranFloat128Math/fma.cpp
index 198fec5d4bc356..a9ac1581002cec 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/fma.cpp
+++ b/flang-rt/lib/FortranFloat128Math/fma.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/fma.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/fma.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/fraction.cpp b/flang-rt/lib/FortranFloat128Math/fraction.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/fraction.cpp
rename to flang-rt/lib/FortranFloat128Math/fraction.cpp
index d4749bf3eb7e0e..39c59a25812abb 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/fraction.cpp
+++ b/flang-rt/lib/FortranFloat128Math/fraction.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/fraction.cpp -------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/fraction.cpp --------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/hypot.cpp b/flang-rt/lib/FortranFloat128Math/hypot.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/hypot.cpp
rename to flang-rt/lib/FortranFloat128Math/hypot.cpp
index 6542bf505060df..c130e204f9951e 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/hypot.cpp
+++ b/flang-rt/lib/FortranFloat128Math/hypot.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/hypot.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/hypot.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/j0.cpp b/flang-rt/lib/FortranFloat128Math/j0.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/j0.cpp
rename to flang-rt/lib/FortranFloat128Math/j0.cpp
index 27e4338cdfc2b0..d6454b56c8a86b 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/j0.cpp
+++ b/flang-rt/lib/FortranFloat128Math/j0.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/j0.cpp -------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/j0.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/j1.cpp b/flang-rt/lib/FortranFloat128Math/j1.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/j1.cpp
rename to flang-rt/lib/FortranFloat128Math/j1.cpp
index d3f897827f9f67..2b7283aea0fe46 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/j1.cpp
+++ b/flang-rt/lib/FortranFloat128Math/j1.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/j1.cpp -------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/j1.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/jn.cpp b/flang-rt/lib/FortranFloat128Math/jn.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/jn.cpp
rename to flang-rt/lib/FortranFloat128Math/jn.cpp
index 681bb5b1ff3ad5..cdc9af9b3dd6a5 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/jn.cpp
+++ b/flang-rt/lib/FortranFloat128Math/jn.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/jn.cpp -------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/jn.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/lgamma.cpp b/flang-rt/lib/FortranFloat128Math/lgamma.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/lgamma.cpp
rename to flang-rt/lib/FortranFloat128Math/lgamma.cpp
index 0426db2e3b98d3..cecf9e90ad29ba 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/lgamma.cpp
+++ b/flang-rt/lib/FortranFloat128Math/lgamma.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/lgamma.cpp ---------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/lgamma.cpp ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/llround.cpp b/flang-rt/lib/FortranFloat128Math/llround.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/llround.cpp
rename to flang-rt/lib/FortranFloat128Math/llround.cpp
index 4c9026cce00283..7853ac10f53e88 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/llround.cpp
+++ b/flang-rt/lib/FortranFloat128Math/llround.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/llround.cpp --------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/llround.cpp ---------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/log.cpp b/flang-rt/lib/FortranFloat128Math/log.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/log.cpp
rename to flang-rt/lib/FortranFloat128Math/log.cpp
index a5a431ae5ffbbb..d705eaf441c31f 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/log.cpp
+++ b/flang-rt/lib/FortranFloat128Math/log.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/log.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/log.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/log10.cpp b/flang-rt/lib/FortranFloat128Math/log10.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/log10.cpp
rename to flang-rt/lib/FortranFloat128Math/log10.cpp
index 9a83f57b6c736d..af61f8762371b9 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/log10.cpp
+++ b/flang-rt/lib/FortranFloat128Math/log10.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/log10.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/log10.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/lround.cpp b/flang-rt/lib/FortranFloat128Math/lround.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/lround.cpp
rename to flang-rt/lib/FortranFloat128Math/lround.cpp
index 65546881157948..24278f1040e9e3 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/lround.cpp
+++ b/flang-rt/lib/FortranFloat128Math/lround.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/lround.cpp ---------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/lround.cpp ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/math-entries.h b/flang-rt/lib/FortranFloat128Math/math-entries.h
similarity index 97%
rename from FortranRuntime/lib/Runtime/Float128Math/math-entries.h
rename to flang-rt/lib/FortranFloat128Math/math-entries.h
index 1449000820f00e..9b13c10836f877 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/math-entries.h
+++ b/flang-rt/lib/FortranFloat128Math/math-entries.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/math-entries.h -----------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/math-entries.h ------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_FLOAT128MATH_MATH_ENTRIES_H_
-#define FORTRAN_RUNTIME_FLOAT128MATH_MATH_ENTRIES_H_
+#ifndef FORTRAN_FORTRANFLOAT128MATH_MATH_ENTRIES_H_
+#define FORTRAN_FORTRANFLOAT128MATH_MATH_ENTRIES_H_
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Common/float128.h"
@@ -222,4 +222,4 @@ DEFINE_SIMPLE_ALIAS(Yn, ynl)
 
 } // namespace Fortran::runtime
 
-#endif /* FORTRAN_RUNTIME_FLOAT128MATH_MATH_ENTRIES_H_ */
+#endif /* FORTRAN_FORTRANFLOAT128MATH_MATH_ENTRIES_H_ */
diff --git a/FortranRuntime/lib/Runtime/Float128Math/mod-real.cpp b/flang-rt/lib/FortranFloat128Math/mod-real.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/mod-real.cpp
rename to flang-rt/lib/FortranFloat128Math/mod-real.cpp
index e3b96d39e76ae6..b3c2b715b21995 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/mod-real.cpp
+++ b/flang-rt/lib/FortranFloat128Math/mod-real.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/mod-real.cpp -------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/mod-real.cpp --------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/modulo-real.cpp b/flang-rt/lib/FortranFloat128Math/modulo-real.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/modulo-real.cpp
rename to flang-rt/lib/FortranFloat128Math/modulo-real.cpp
index 8edf59e9f59dd4..f5e3cf8a259a73 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/modulo-real.cpp
+++ b/flang-rt/lib/FortranFloat128Math/modulo-real.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/modulo-real.cpp ----------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/modulo-real.cpp -----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/nearest.cpp b/flang-rt/lib/FortranFloat128Math/nearest.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/nearest.cpp
rename to flang-rt/lib/FortranFloat128Math/nearest.cpp
index 8b9f142d79ff93..eb34c2ddb6ab48 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/nearest.cpp
+++ b/flang-rt/lib/FortranFloat128Math/nearest.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/nearest.cpp --------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/nearest.cpp ---------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/norm2.cpp b/flang-rt/lib/FortranFloat128Math/norm2.cpp
similarity index 94%
rename from FortranRuntime/lib/Runtime/Float128Math/norm2.cpp
rename to flang-rt/lib/FortranFloat128Math/norm2.cpp
index a0c26e40de0064..d000fde1bb0bea 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/norm2.cpp
+++ b/flang-rt/lib/FortranFloat128Math/norm2.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/norm2.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/norm2.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/numeric-template-specs.h b/flang-rt/lib/FortranFloat128Math/numeric-template-specs.h
similarity index 84%
rename from FortranRuntime/lib/Runtime/Float128Math/numeric-template-specs.h
rename to flang-rt/lib/FortranFloat128Math/numeric-template-specs.h
index 2a843df2d1d861..f34ee5f4e3a8de 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/numeric-template-specs.h
+++ b/flang-rt/lib/FortranFloat128Math/numeric-template-specs.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/numeric-template-specs.h -------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/numeric-template-specs.h --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_FLOAT128MATH_NUMERIC_TEMPLATE_SPECS_H_
-#define FORTRAN_RUNTIME_FLOAT128MATH_NUMERIC_TEMPLATE_SPECS_H_
+#ifndef FORTRAN_FORTRANFLOAT128MATH_NUMERIC_TEMPLATE_SPECS_H_
+#define FORTRAN_FORTRANFLOAT128MATH_NUMERIC_TEMPLATE_SPECS_H_
 
 #include "math-entries.h"
 #include "numeric-templates.h"
@@ -52,4 +52,4 @@ template <> struct SQRTTy<F128Type> {
 };
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_FLOAT128MATH_NUMERIC_TEMPLATE_SPECS_H_ */
+#endif /* FORTRAN_FORTRANFLOAT128MATH_NUMERIC_TEMPLATE_SPECS_H_ */
diff --git a/FortranRuntime/lib/Runtime/Float128Math/pow.cpp b/flang-rt/lib/FortranFloat128Math/pow.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/pow.cpp
rename to flang-rt/lib/FortranFloat128Math/pow.cpp
index c11978ca068f23..f5deb00a556f48 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/pow.cpp
+++ b/flang-rt/lib/FortranFloat128Math/pow.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/pow.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/pow.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/random.cpp b/flang-rt/lib/FortranFloat128Math/random.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/random.cpp
rename to flang-rt/lib/FortranFloat128Math/random.cpp
index a9dc3c7a82b673..3a01c2c88b1d66 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/random.cpp
+++ b/flang-rt/lib/FortranFloat128Math/random.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/random.cpp ---------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/random.cpp ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/round.cpp b/flang-rt/lib/FortranFloat128Math/round.cpp
similarity index 92%
rename from FortranRuntime/lib/Runtime/Float128Math/round.cpp
rename to flang-rt/lib/FortranFloat128Math/round.cpp
index 5a9366b3af4785..3453f4ea8a1a26 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/round.cpp
+++ b/flang-rt/lib/FortranFloat128Math/round.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/round.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/round.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/rrspacing.cpp b/flang-rt/lib/FortranFloat128Math/rrspacing.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/rrspacing.cpp
rename to flang-rt/lib/FortranFloat128Math/rrspacing.cpp
index 2c501b3512c215..0809815027f859 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/rrspacing.cpp
+++ b/flang-rt/lib/FortranFloat128Math/rrspacing.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/rrspacing.cpp ------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/rrspacing.cpp -------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/scale.cpp b/flang-rt/lib/FortranFloat128Math/scale.cpp
similarity index 92%
rename from FortranRuntime/lib/Runtime/Float128Math/scale.cpp
rename to flang-rt/lib/FortranFloat128Math/scale.cpp
index 859c955b8114e0..37528330bfb115 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/scale.cpp
+++ b/flang-rt/lib/FortranFloat128Math/scale.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/scale.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/scale.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/set-exponent.cpp b/flang-rt/lib/FortranFloat128Math/set-exponent.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/set-exponent.cpp
rename to flang-rt/lib/FortranFloat128Math/set-exponent.cpp
index 52258182871a14..52f8f08f7003ef 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/set-exponent.cpp
+++ b/flang-rt/lib/FortranFloat128Math/set-exponent.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/set-exponent.cpp ---------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/set-exponent.cpp ----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/sin.cpp b/flang-rt/lib/FortranFloat128Math/sin.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/sin.cpp
rename to flang-rt/lib/FortranFloat128Math/sin.cpp
index 99aa4095c8cf1a..1a24e7c57ba469 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/sin.cpp
+++ b/flang-rt/lib/FortranFloat128Math/sin.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/sin.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/sin.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/sinh.cpp b/flang-rt/lib/FortranFloat128Math/sinh.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/sinh.cpp
rename to flang-rt/lib/FortranFloat128Math/sinh.cpp
index a7dfe36737de43..7a4127cee970cd 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/sinh.cpp
+++ b/flang-rt/lib/FortranFloat128Math/sinh.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/sinh.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/sinh.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/spacing.cpp b/flang-rt/lib/FortranFloat128Math/spacing.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/spacing.cpp
rename to flang-rt/lib/FortranFloat128Math/spacing.cpp
index 66a01851965840..d3ed077d5412dc 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/spacing.cpp
+++ b/flang-rt/lib/FortranFloat128Math/spacing.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/spacing.cpp --------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/spacing.cpp ---------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/sqrt.cpp b/flang-rt/lib/FortranFloat128Math/sqrt.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/sqrt.cpp
rename to flang-rt/lib/FortranFloat128Math/sqrt.cpp
index cbc1e503d50fd9..a9f5246f35388f 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/sqrt.cpp
+++ b/flang-rt/lib/FortranFloat128Math/sqrt.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/sqrt.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/sqrt.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/tan.cpp b/flang-rt/lib/FortranFloat128Math/tan.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/tan.cpp
rename to flang-rt/lib/FortranFloat128Math/tan.cpp
index dbe4627f585f14..dc386c5be6ab74 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/tan.cpp
+++ b/flang-rt/lib/FortranFloat128Math/tan.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/tan.cpp ------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/tan.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/tanh.cpp b/flang-rt/lib/FortranFloat128Math/tanh.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/tanh.cpp
rename to flang-rt/lib/FortranFloat128Math/tanh.cpp
index 37e40966ced722..5f8af3f1cd8d77 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/tanh.cpp
+++ b/flang-rt/lib/FortranFloat128Math/tanh.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/tanh.cpp -----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/tanh.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/tgamma.cpp b/flang-rt/lib/FortranFloat128Math/tgamma.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/tgamma.cpp
rename to flang-rt/lib/FortranFloat128Math/tgamma.cpp
index 07a019c6d9971f..b1a42cdc5d0f41 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/tgamma.cpp
+++ b/flang-rt/lib/FortranFloat128Math/tgamma.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/tgamma.cpp ---------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/tgamma.cpp ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/trunc.cpp b/flang-rt/lib/FortranFloat128Math/trunc.cpp
similarity index 91%
rename from FortranRuntime/lib/Runtime/Float128Math/trunc.cpp
rename to flang-rt/lib/FortranFloat128Math/trunc.cpp
index 9f38bdc18e73c4..455204ece3b2f6 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/trunc.cpp
+++ b/flang-rt/lib/FortranFloat128Math/trunc.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/trunc.cpp ----------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/trunc.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/y0.cpp b/flang-rt/lib/FortranFloat128Math/y0.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/y0.cpp
rename to flang-rt/lib/FortranFloat128Math/y0.cpp
index 6eaa3396e7ea07..58bd71105efea6 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/y0.cpp
+++ b/flang-rt/lib/FortranFloat128Math/y0.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/y0.cpp -------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/y0.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/y1.cpp b/flang-rt/lib/FortranFloat128Math/y1.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/y1.cpp
rename to flang-rt/lib/FortranFloat128Math/y1.cpp
index c9f48ea0e26546..5d7b48e276b6f9 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/y1.cpp
+++ b/flang-rt/lib/FortranFloat128Math/y1.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/y1.cpp -------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/y1.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/Float128Math/yn.cpp b/flang-rt/lib/FortranFloat128Math/yn.cpp
similarity index 90%
rename from FortranRuntime/lib/Runtime/Float128Math/yn.cpp
rename to flang-rt/lib/FortranFloat128Math/yn.cpp
index 6bc5f4996a88d5..9f19861931d84c 100644
--- a/FortranRuntime/lib/Runtime/Float128Math/yn.cpp
+++ b/flang-rt/lib/FortranFloat128Math/yn.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/Float128Math/yn.cpp -------------------------*- C++ -*-===//
+//===-- lib/FortranFloat128Math/yn.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Testing/CMakeLists.txt b/flang-rt/lib/Testing/CMakeLists.txt
similarity index 89%
rename from FortranRuntime/lib/Testing/CMakeLists.txt
rename to flang-rt/lib/Testing/CMakeLists.txt
index 41ad0d7314dd37..bdfca0ee9d3f23 100644
--- a/FortranRuntime/lib/Testing/CMakeLists.txt
+++ b/flang-rt/lib/Testing/CMakeLists.txt
@@ -11,7 +11,7 @@ file(GLOB_RECURSE public_headers
   "${FLANG_SOURCE_DIR}/lib/Testing/*.h"
 )
 
-add_fortranruntime_library(NonGTestTesting EXCLUDE_FROM_ALL LINK_TO_LLVM
+add_flangrt_library(NonGTestTesting EXCLUDE_FROM_ALL LINK_TO_LLVM
   ${FLANG_SOURCE_DIR}/lib/Testing/testing.cpp
   ${FLANG_SOURCE_DIR}/lib/Testing/fp-testing.cpp
  ADDITIONAL_HEADERS
diff --git a/FortranRuntime/lib/Runtime/CMakeLists.txt b/flang-rt/lib/flang_rt/CMakeLists.txt
similarity index 66%
rename from FortranRuntime/lib/Runtime/CMakeLists.txt
rename to flang-rt/lib/flang_rt/CMakeLists.txt
index 1db5520d5eaedf..860152c39c7204 100644
--- a/FortranRuntime/lib/Runtime/CMakeLists.txt
+++ b/flang-rt/lib/flang_rt/CMakeLists.txt
@@ -1,4 +1,4 @@
-#===-- lib/Runtime/CMakeLists.txt ------------------------------------------===#
+#===-- lib/flang_rt/CMakeLists.txt -----------------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
@@ -6,7 +6,7 @@
 #
 #===------------------------------------------------------------------------===#
 
-include(AddFortranOffloadRuntime)
+include(AddFlangRTOffload)
 
 # List of files that are buildable for all devices.
 set(supported_sources
@@ -73,7 +73,7 @@ set(host_sources
   exceptions.cpp
   execute.cpp
   extensions.cpp
-  iso_fortran_env_impl.f90
+  ${FLANG_SOURCE_DIR}/module/iso_fortran_env_impl.f90
   main.cpp
   random.cpp
   reduce.cpp
@@ -84,18 +84,17 @@ set(host_sources
 )
 
 file(GLOB_RECURSE public_headers
-  "${FLANGRUNTIME_SOURCE_DIR}/include/flang/Runtime/*.h"
-  "${FLANGRUNTIME_SOURCE_DIR}/include/flang/Common/*.h"
+  "${FLANGRT_SOURCE_DIR}/include/flang/Runtime/*.h"
+  "${FLANGRT_SOURCE_DIR}/include/flang/Common/*.h"
   )
 
 file(GLOB_RECURSE private_headers
-  "${FLANGRUNTIME_SOURCE_DIR}/lib/Runtime/*.h"
-  "${FLANGRUNTIME_SOURCE_DIR}/lib/Common/*.h"
+  "${FLANGRT_SOURCE_DIR}/lib/Runtime/*.h"
+  "${FLANGRT_SOURCE_DIR}/lib/Common/*.h"
   )
 
 
-add_subdirectory(Float128Math)
-
+# Import changes from sibling FortranFloat128Math
 get_target_property(f128_sources
   FortranFloat128MathILib INTERFACE_SOURCES
   )
@@ -117,23 +116,23 @@ endif ()
 set(sources ${supported_sources} ${host_sources} ${f128_sources})
 
 if (NOT WIN32)
-  add_fortranruntime_library(FortranRuntime STATIC
+  add_flangrt_library(flang_rt STATIC
     ${sources}
     INSTALL_WITH_TOOLCHAIN
     ADDITIONAL_HEADERS ${public_headers} ${private_headers}
   )
 
-  enable_cuda_compilation(FortranRuntime "${supported_sources}")
+  enable_cuda_compilation(flang_rt "${supported_sources}")
   enable_omp_offload_compilation("${supported_sources}")
 
-  # For unittests that link to FortranRuntime. Should link to the static version
+  # For unittests that depend on flang_rt. Should link to the static version
   # of the library.
-  add_library(FortranRuntime.static ALIAS FortranRuntime)
-  add_library(FortranRuntime.unittest ALIAS FortranRuntime)
+  add_library(flang_rt.static ALIAS flang_rt)
+  add_library(flang_rt.unittest ALIAS flang_rt)
 else()
-  function (add_win_fortranruntime_library libtype suffix msvc_lib)
-    set(name "FortranRuntime.${suffix}")
-    add_fortranruntime_library(${name} ${libtype}
+  function (add_win_flangrt_library libtype suffix msvc_lib)
+    set(name "flang_rt.${suffix}")
+    add_flangrt_library(${name} ${libtype}
         ${sources}
         ${ARGN}
         INSTALL_WITH_TOOLCHAIN
@@ -148,32 +147,28 @@ else()
           Fortran_MODULE_DIRECTORY "module.${suffix}"
       )
 
-    enable_cuda_compilation(FortranRuntime "${supported_sources}")
+    enable_cuda_compilation(${name} "${supported_sources}")
     enable_omp_offload_compilation("${supported_sources}")
   endfunction ()
 
-  add_win_fortranruntime_library(STATIC static     MultiThreaded)
-  add_win_fortranruntime_library(STATIC static_dbg MultiThreadedDebug)
+  add_win_flangrt_library(STATIC static     MultiThreaded)
+  add_win_flangrt_library(STATIC static_dbg MultiThreadedDebug)
 
   # unittests link against LLVMSupport which is compiled with /MD
-  add_win_fortranruntime_library(STATIC unittest   MultiThreadedDLL EXCLUDE_FROM_ALL)
+  add_win_flangrt_library(STATIC unittest   MultiThreadedDLL EXCLUDE_FROM_ALL)
 
   # FIXME: Before DLL versions of the runtime can be used, exported definitions
   # must be annotated with __declspec(dllexport).
-  add_win_fortranruntime_library(SHARED dynamic     MultiThreadedDLL)
-  add_win_fortranruntime_library(SHARED dynamic_dbg MultiThreadedDebugDLL)
+  add_win_flangrt_library(SHARED dynamic     MultiThreadedDLL)
+  add_win_flangrt_library(SHARED dynamic_dbg MultiThreadedDebugDLL)
 
   # Target for building all versions of the runtime
-  add_custom_target(FortranRuntime)
-  set_target_properties(FortranRuntime PROPERTIES FOLDER "Fortran Runtime/Meta")
-  add_dependencies(FortranRuntime
-      FortranRuntime.static
-      FortranRuntime.static_dbg
-      FortranRuntime.dynamic
-      FortranRuntime.dynamic_dbg
+  add_custom_target(flang_rt)
+  set_target_properties(flang_rt PROPERTIES FOLDER "Fortran Runtime/Meta")
+  add_dependencies(flang_rt
+      flang_rt.static
+      flang_rt.static_dbg
+      flang_rt.dynamic
+      flang_rt.dynamic_dbg
     )
 endif()
-
-if (FORTRANRUNTIME_ENABLE_CUF)
-  add_subdirectory(CUDA)
-endif()
diff --git a/FortranRuntime/lib/Runtime/ISO_Fortran_binding.cpp b/flang-rt/lib/flang_rt/ISO_Fortran_binding.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/ISO_Fortran_binding.cpp
rename to flang-rt/lib/flang_rt/ISO_Fortran_binding.cpp
index 997226b08e96a6..37bc1b9dfe426b 100644
--- a/FortranRuntime/lib/Runtime/ISO_Fortran_binding.cpp
+++ b/flang-rt/lib/flang_rt/ISO_Fortran_binding.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/ISO_Fortran_binding.cpp ---------------------*- C++ -*-===//
+//===-- lib/flang_rt/ISO_Fortran_binding.cpp --------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,9 +9,9 @@
 // Implements the required interoperability API from ISO_Fortran_binding.h
 // as specified in section 18.5.5 of Fortran 2018.
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
 #include "ISO_Fortran_util.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "terminator.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Runtime/pointer.h"
diff --git a/FortranRuntime/lib/Runtime/ISO_Fortran_util.h b/flang-rt/lib/flang_rt/ISO_Fortran_util.h
similarity index 91%
rename from FortranRuntime/lib/Runtime/ISO_Fortran_util.h
rename to flang-rt/lib/flang_rt/ISO_Fortran_util.h
index e418266dddccc7..a7bb1d21679063 100644
--- a/FortranRuntime/lib/Runtime/ISO_Fortran_util.h
+++ b/flang-rt/lib/flang_rt/ISO_Fortran_util.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/ISO_Fortran_util.h --------------------------*- C++ -*-===//
+//===-- lib/flang_rt/ISO_Fortran_util.h -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,13 +6,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_ISO_FORTRAN_UTIL_H_
-#define FORTRAN_RUNTIME_ISO_FORTRAN_UTIL_H_
+#ifndef FORTRAN_FLANG_RT_ISO_FORTRAN_UTIL_H_
+#define FORTRAN_FLANG_RT_ISO_FORTRAN_UTIL_H_
 
 // Internal utils for establishing CFI_cdesc_t descriptors.
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "terminator.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include <cstdlib>
@@ -99,4 +99,4 @@ static inline RT_API_ATTRS void EstablishDescriptor(CFI_cdesc_t *descriptor,
   }
 }
 } // namespace Fortran::ISO
-#endif /* FORTRAN_RUNTIME_ISO_FORTRAN_UTIL_H_ */
+#endif /* FORTRAN_FLANG_RT_ISO_FORTRAN_UTIL_H_ */
diff --git a/FortranRuntime/lib/Runtime/allocatable.cpp b/flang-rt/lib/flang_rt/allocatable.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/allocatable.cpp
rename to flang-rt/lib/flang_rt/allocatable.cpp
index 4a3b89f4879c12..b9be74f8cb6f1b 100644
--- a/FortranRuntime/lib/Runtime/allocatable.cpp
+++ b/flang-rt/lib/flang_rt/allocatable.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/allocatable.cpp -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/allocatable.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/allocatable.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "assign-impl.h"
 #include "derived.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "stat.h"
 #include "terminator.h"
 #include "type-info.h"
diff --git a/FortranRuntime/lib/Runtime/allocator-registry.cpp b/flang-rt/lib/flang_rt/allocator-registry.cpp
similarity index 85%
rename from FortranRuntime/lib/Runtime/allocator-registry.cpp
rename to flang-rt/lib/flang_rt/allocator-registry.cpp
index 17883e5c54870d..a0e6fd8eadc856 100644
--- a/FortranRuntime/lib/Runtime/allocator-registry.cpp
+++ b/flang-rt/lib/flang_rt/allocator-registry.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/allocator-registry.cpp ----------------------*- C++ -*-===//
+//===-- lib/flang_rt/allocator-registry.cpp ---------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,16 +6,16 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/allocator-registry.h"
+#include "flang-rt/flang_rt/allocator-registry.h"
 #include "terminator.h"
 
 namespace Fortran::runtime {
 
-#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#ifndef FLANGRT_NO_GLOBAL_VAR_DEFS
 RT_OFFLOAD_VAR_GROUP_BEGIN
 RT_VAR_ATTRS AllocatorRegistry allocatorRegistry;
 RT_OFFLOAD_VAR_GROUP_END
-#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#endif // FLANGRT_NO_GLOBAL_VAR_DEFS
 
 RT_OFFLOAD_API_GROUP_BEGIN
 RT_API_ATTRS void AllocatorRegistry::Register(int pos, Allocator_t allocator) {
diff --git a/FortranRuntime/lib/Runtime/array-constructor.cpp b/flang-rt/lib/flang_rt/array-constructor.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/array-constructor.cpp
rename to flang-rt/lib/flang_rt/array-constructor.cpp
index 002dfba2c066f5..daaa1e3b04a3b6 100644
--- a/FortranRuntime/lib/Runtime/array-constructor.cpp
+++ b/flang-rt/lib/flang_rt/array-constructor.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/array-constructor.cpp -----------------------*- C++ -*-===//
+//===-- lib/flang_rt/array-constructor.cpp ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,9 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/array-constructor.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/array-constructor.h"
 #include "derived.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "type-info.h"
diff --git a/FortranRuntime/lib/Runtime/assign-impl.h b/flang-rt/lib/flang_rt/assign-impl.h
similarity index 100%
rename from FortranRuntime/lib/Runtime/assign-impl.h
rename to flang-rt/lib/flang_rt/assign-impl.h
diff --git a/FortranRuntime/lib/Runtime/assign.cpp b/flang-rt/lib/flang_rt/assign.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/assign.cpp
rename to flang-rt/lib/flang_rt/assign.cpp
index 3a1486ace928a2..4916fc48888189 100644
--- a/FortranRuntime/lib/Runtime/assign.cpp
+++ b/flang-rt/lib/flang_rt/assign.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/assign.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/assign.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/assign.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "assign-impl.h"
 #include "derived.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "stat.h"
 #include "terminator.h"
 #include "tools.h"
diff --git a/FortranRuntime/lib/Runtime/buffer.cpp b/flang-rt/lib/flang_rt/buffer.cpp
similarity index 93%
rename from FortranRuntime/lib/Runtime/buffer.cpp
rename to flang-rt/lib/flang_rt/buffer.cpp
index ce78fe34503c46..9913cdf2e7ec40 100644
--- a/FortranRuntime/lib/Runtime/buffer.cpp
+++ b/flang-rt/lib/flang_rt/buffer.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/buffer.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/buffer.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/buffer.h b/flang-rt/lib/flang_rt/buffer.h
similarity index 97%
rename from FortranRuntime/lib/Runtime/buffer.h
rename to flang-rt/lib/flang_rt/buffer.h
index 52df0f10813c25..eb9b0712819a6c 100644
--- a/FortranRuntime/lib/Runtime/buffer.h
+++ b/flang-rt/lib/flang_rt/buffer.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/buffer.h ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/buffer.h -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,10 +8,10 @@
 
 // External file buffering
 
-#ifndef FORTRAN_RUNTIME_BUFFER_H_
-#define FORTRAN_RUNTIME_BUFFER_H_
+#ifndef FORTRAN_FLANG_RT_BUFFER_H_
+#define FORTRAN_FLANG_RT_BUFFER_H_
 
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "io-error.h"
 #include "flang/Runtime/freestanding-tools.h"
 #include <algorithm>
@@ -221,4 +221,4 @@ template <typename STORE, std::size_t minBuffer = 65536> class FileFrame {
   bool dirty_{false};
 };
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_BUFFER_H_ */
+#endif /* FORTRAN_FLANG_RT_BUFFER_H_ */
diff --git a/FortranRuntime/lib/Runtime/character.cpp b/flang-rt/lib/flang_rt/character.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/character.cpp
rename to flang-rt/lib/flang_rt/character.cpp
index 1f3edd6e80392e..aeb26098c399c8 100644
--- a/FortranRuntime/lib/Runtime/character.cpp
+++ b/flang-rt/lib/flang_rt/character.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/character.cpp -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/character.cpp ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/character.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Common/bit-population-count.h"
diff --git a/FortranRuntime/lib/Runtime/command.cpp b/flang-rt/lib/flang_rt/command.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/command.cpp
rename to flang-rt/lib/flang_rt/command.cpp
index 64b2e62461dd58..5c7497518f3da3 100644
--- a/FortranRuntime/lib/Runtime/command.cpp
+++ b/flang-rt/lib/flang_rt/command.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/command.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/command.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/command.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "environment.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "stat.h"
 #include "terminator.h"
 #include "tools.h"
diff --git a/FortranRuntime/lib/Runtime/complex-powi.cpp b/flang-rt/lib/flang_rt/complex-powi.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/complex-powi.cpp
rename to flang-rt/lib/flang_rt/complex-powi.cpp
index 2eacf56386b193..90013c117aea41 100644
--- a/FortranRuntime/lib/Runtime/complex-powi.cpp
+++ b/flang-rt/lib/flang_rt/complex-powi.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/complex-powi.cpp ----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/complex-powi.cpp ---------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/complex-reduction.c b/flang-rt/lib/flang_rt/complex-reduction.c
similarity index 98%
rename from FortranRuntime/lib/Runtime/complex-reduction.c
rename to flang-rt/lib/flang_rt/complex-reduction.c
index 138174e9122b1c..23f1edb58b2d4e 100644
--- a/FortranRuntime/lib/Runtime/complex-reduction.c
+++ b/flang-rt/lib/flang_rt/complex-reduction.c
@@ -1,4 +1,4 @@
-/*===-- lib/Runtime/complex-reduction.c -----------------------------*- C -*-===
+/*===-- lib/flang_rt/complex-reduction.c ----------------------------*- C -*-===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/complex-reduction.h b/flang-rt/lib/flang_rt/complex-reduction.h
similarity index 97%
rename from FortranRuntime/lib/Runtime/complex-reduction.h
rename to flang-rt/lib/flang_rt/complex-reduction.h
index e8e287215b7d97..b386b25cd0fff8 100644
--- a/FortranRuntime/lib/Runtime/complex-reduction.h
+++ b/flang-rt/lib/flang_rt/complex-reduction.h
@@ -1,4 +1,4 @@
-/*===-- lib/Runtime/complex-reduction.h -----------------------------*- C -*-===
+/*===-- lib/flang_rt/complex-reduction.h ----------------------------*- C -*-===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
@@ -11,8 +11,8 @@
  * with C++ build compilers that don't support C's _Complex.
  */
 
-#ifndef FORTRAN_RUNTIME_COMPLEX_REDUCTION_H_
-#define FORTRAN_RUNTIME_COMPLEX_REDUCTION_H_
+#ifndef FORTRAN_FLANG_RT_COMPLEX_REDUCTION_H_
+#define FORTRAN_FLANG_RT_COMPLEX_REDUCTION_H_
 
 #include "flang/Common/float128.h"
 #include "flang/Runtime/entry-names.h"
@@ -155,4 +155,4 @@ void RTNAME(ReduceComplex16DimValue)(
     REDUCE_DIM_ARGS(CFloat128ComplexType, CFloat128ComplexType_value_op));
 #endif
 
-#endif /* FORTRAN_RUNTIME_COMPLEX_REDUCTION_H_ */
+#endif /* FORTRAN_FLANG_RT_COMPLEX_REDUCTION_H_ */
diff --git a/FortranRuntime/lib/Runtime/connection.cpp b/flang-rt/lib/flang_rt/connection.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/connection.cpp
rename to flang-rt/lib/flang_rt/connection.cpp
index f9e91f1f193ba0..d623190f22f6f9 100644
--- a/FortranRuntime/lib/Runtime/connection.cpp
+++ b/flang-rt/lib/flang_rt/connection.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/connection.cpp ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/connection.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/connection.h b/flang-rt/lib/flang_rt/connection.h
similarity index 96%
rename from FortranRuntime/lib/Runtime/connection.h
rename to flang-rt/lib/flang_rt/connection.h
index e078bfb9f0f7e7..f8b9b3f9debcda 100644
--- a/FortranRuntime/lib/Runtime/connection.h
+++ b/flang-rt/lib/flang_rt/connection.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/connection.h --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/connection.h -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Fortran I/O connection state (abstracted over internal & external units)
 
-#ifndef FORTRAN_RUNTIME_CONNECTION_H_
-#define FORTRAN_RUNTIME_CONNECTION_H_
+#ifndef FORTRAN_FLANG_RT_CONNECTION_H_
+#define FORTRAN_FLANG_RT_CONNECTION_H_
 
 #include "format.h"
 #include "flang/Common/optional.h"
@@ -124,4 +124,4 @@ class SavedPosition {
 };
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_CONNECTION_H_ */
+#endif /* FORTRAN_FLANG_RT_CONNECTION_H_ */
diff --git a/FortranRuntime/lib/Runtime/copy.cpp b/flang-rt/lib/flang_rt/copy.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/copy.cpp
rename to flang-rt/lib/flang_rt/copy.cpp
index 1049b925f68e5c..fc5c0af6b95851 100644
--- a/FortranRuntime/lib/Runtime/copy.cpp
+++ b/flang-rt/lib/flang_rt/copy.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/copy.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/copy.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "copy.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "stack.h"
 #include "terminator.h"
 #include "type-info.h"
diff --git a/FortranRuntime/lib/Runtime/copy.h b/flang-rt/lib/flang_rt/copy.h
similarity index 78%
rename from FortranRuntime/lib/Runtime/copy.h
rename to flang-rt/lib/flang_rt/copy.h
index 3d179d0bec91a7..8f27c3a90b7847 100644
--- a/FortranRuntime/lib/Runtime/copy.h
+++ b/flang-rt/lib/flang_rt/copy.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/copy.h --------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/copy.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,10 +9,10 @@
 // Utilities that copy data in a type-aware fashion, allocating & duplicating
 // allocatable/automatic components of derived types along the way.
 
-#ifndef FORTRAN_RUNTIME_COPY_H_
-#define FORTRAN_RUNTIME_COPY_H_
+#ifndef FORTRAN_FLANG_RT_COPY_H_
+#define FORTRAN_FLANG_RT_COPY_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 
 namespace Fortran::runtime {
 
@@ -22,4 +22,4 @@ RT_API_ATTRS void CopyElement(const Descriptor &to, const SubscriptValue toAt[],
     const Descriptor &from, const SubscriptValue fromAt[], Terminator &);
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_COPY_H_ */
+#endif /* FORTRAN_FLANG_RT_COPY_H_ */
diff --git a/FortranRuntime/lib/Runtime/derived-api.cpp b/flang-rt/lib/flang_rt/derived-api.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/derived-api.cpp
rename to flang-rt/lib/flang_rt/derived-api.cpp
index 176fc0849f25cf..faf24508981bae 100644
--- a/FortranRuntime/lib/Runtime/derived-api.cpp
+++ b/flang-rt/lib/flang_rt/derived-api.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/derived-api.cpp -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/derived-api.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/derived-api.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "derived.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "type-info.h"
diff --git a/FortranRuntime/lib/Runtime/derived.cpp b/flang-rt/lib/flang_rt/derived.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/derived.cpp
rename to flang-rt/lib/flang_rt/derived.cpp
index cb2dca24bb4758..9b17a0d437375c 100644
--- a/FortranRuntime/lib/Runtime/derived.cpp
+++ b/flang-rt/lib/flang_rt/derived.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/derived.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/derived.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "derived.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "stat.h"
 #include "terminator.h"
 #include "tools.h"
diff --git a/FortranRuntime/lib/Runtime/derived.h b/flang-rt/lib/flang_rt/derived.h
similarity index 88%
rename from FortranRuntime/lib/Runtime/derived.h
rename to flang-rt/lib/flang_rt/derived.h
index e03e657f01cee9..3d6563f39c0663 100644
--- a/FortranRuntime/lib/Runtime/derived.h
+++ b/flang-rt/lib/flang_rt/derived.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/derived.h -----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/derived.h ----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Internal runtime utilities for derived type operations.
 
-#ifndef FORTRAN_RUNTIME_DERIVED_H_
-#define FORTRAN_RUNTIME_DERIVED_H_
+#ifndef FORTRAN_FLANG_RT_DERIVED_H_
+#define FORTRAN_FLANG_RT_DERIVED_H_
 
 #include "flang/Common/api-attrs.h"
 
@@ -40,4 +40,4 @@ RT_API_ATTRS void Destroy(const Descriptor &, bool finalize,
 RT_API_ATTRS bool HasDynamicComponent(const Descriptor &);
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_DERIVED_H_ */
+#endif /* FORTRAN_FLANG_RT_DERIVED_H_ */
diff --git a/FortranRuntime/lib/Runtime/descriptor-io.cpp b/flang-rt/lib/flang_rt/descriptor-io.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/descriptor-io.cpp
rename to flang-rt/lib/flang_rt/descriptor-io.cpp
index 896fad16a67e8a..c5cfa4d7fc5972 100644
--- a/FortranRuntime/lib/Runtime/descriptor-io.cpp
+++ b/flang-rt/lib/flang_rt/descriptor-io.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/descriptor-io.cpp ---------------------------*- C++ -*-===//
+//===-- lib/flang_rt/descriptor-io.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/descriptor-io.h b/flang-rt/lib/flang_rt/descriptor-io.h
similarity index 98%
rename from FortranRuntime/lib/Runtime/descriptor-io.h
rename to flang-rt/lib/flang_rt/descriptor-io.h
index 30d1bd48457728..2e48b4a0353e2a 100644
--- a/FortranRuntime/lib/Runtime/descriptor-io.h
+++ b/flang-rt/lib/flang_rt/descriptor-io.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/descriptor-io.h -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/descriptor-io.h ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,17 +6,17 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_DESCRIPTOR_IO_H_
-#define FORTRAN_RUNTIME_DESCRIPTOR_IO_H_
+#ifndef FORTRAN_FLANG_RT_DESCRIPTOR_IO_H_
+#define FORTRAN_FLANG_RT_DESCRIPTOR_IO_H_
 
 // Implementation of I/O data list item transfers based on descriptors.
 // (All I/O items come through here so that the code is exercised for test;
 // some scalar I/O data transfer APIs could be changed to bypass their use
 // of descriptors in the future for better efficiency.)
 
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "edit-input.h"
 #include "edit-output.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "io-stmt.h"
 #include "namelist.h"
 #include "terminator.h"
@@ -608,4 +608,4 @@ static RT_API_ATTRS bool DescriptorIO(IoStatementState &io,
   return false;
 }
 } // namespace Fortran::runtime::io::descr
-#endif /* FORTRAN_RUNTIME_DESCRIPTOR_IO_H_ */
+#endif /* FORTRAN_FLANG_RT_DESCRIPTOR_IO_H_ */
diff --git a/FortranRuntime/lib/Runtime/descriptor.cpp b/flang-rt/lib/flang_rt/descriptor.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/descriptor.cpp
rename to flang-rt/lib/flang_rt/descriptor.cpp
index 96fd48eb6687a9..77536e760ad1cd 100644
--- a/FortranRuntime/lib/Runtime/descriptor.cpp
+++ b/flang-rt/lib/flang_rt/descriptor.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/descriptor.cpp ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/descriptor.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,10 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/allocator-registry.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "ISO_Fortran_util.h"
 #include "derived.h"
+#include "flang-rt/flang_rt/allocator-registry.h"
 #include "memory.h"
 #include "stat.h"
 #include "terminator.h"
diff --git a/FortranRuntime/lib/Runtime/dot-product.cpp b/flang-rt/lib/flang_rt/dot-product.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/dot-product.cpp
rename to flang-rt/lib/flang_rt/dot-product.cpp
index 2992cbb1f39ad6..01e15ad331d7c4 100644
--- a/FortranRuntime/lib/Runtime/dot-product.cpp
+++ b/flang-rt/lib/flang_rt/dot-product.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/dot-product.cpp -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/dot-product.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "float.h"
 #include "terminator.h"
 #include "tools.h"
diff --git a/FortranRuntime/lib/Runtime/edit-input.cpp b/flang-rt/lib/flang_rt/edit-input.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/edit-input.cpp
rename to flang-rt/lib/flang_rt/edit-input.cpp
index 6ebb0e7aca4ade..9e3f102cf86684 100644
--- a/FortranRuntime/lib/Runtime/edit-input.cpp
+++ b/flang-rt/lib/flang_rt/edit-input.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/edit-input.cpp ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/edit-input.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/edit-input.h b/flang-rt/lib/flang_rt/edit-input.h
similarity index 90%
rename from FortranRuntime/lib/Runtime/edit-input.h
rename to flang-rt/lib/flang_rt/edit-input.h
index f88f6daa47be79..59f601afa306a3 100644
--- a/FortranRuntime/lib/Runtime/edit-input.h
+++ b/flang-rt/lib/flang_rt/edit-input.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/edit-input.h --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/edit-input.h -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_EDIT_INPUT_H_
-#define FORTRAN_RUNTIME_EDIT_INPUT_H_
+#ifndef FORTRAN_FLANG_RT_EDIT_INPUT_H_
+#define FORTRAN_FLANG_RT_EDIT_INPUT_H_
 
 #include "format.h"
 #include "io-stmt.h"
@@ -50,4 +50,4 @@ extern template RT_API_ATTRS bool EditCharacterInput(
     IoStatementState &, const DataEdit &, char32_t *, std::size_t);
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_EDIT_INPUT_H_ */
+#endif /* FORTRAN_FLANG_RT_EDIT_INPUT_H_ */
diff --git a/FortranRuntime/lib/Runtime/edit-output.cpp b/flang-rt/lib/flang_rt/edit-output.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/edit-output.cpp
rename to flang-rt/lib/flang_rt/edit-output.cpp
index ccaf8085f016fd..2e353f1ad80a21 100644
--- a/FortranRuntime/lib/Runtime/edit-output.cpp
+++ b/flang-rt/lib/flang_rt/edit-output.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/edit-output.cpp -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/edit-output.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/edit-output.h b/flang-rt/lib/flang_rt/edit-output.h
similarity index 96%
rename from FortranRuntime/lib/Runtime/edit-output.h
rename to flang-rt/lib/flang_rt/edit-output.h
index 7e6c6cdedde3ac..325658b4a25dc6 100644
--- a/FortranRuntime/lib/Runtime/edit-output.h
+++ b/flang-rt/lib/flang_rt/edit-output.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/edit-output.h -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/edit-output.h ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_EDIT_OUTPUT_H_
-#define FORTRAN_RUNTIME_EDIT_OUTPUT_H_
+#ifndef FORTRAN_FLANG_RT_EDIT_OUTPUT_H_
+#define FORTRAN_FLANG_RT_EDIT_OUTPUT_H_
 
 // Output data editing templates implementing the FORMAT data editing
 // descriptors E, EN, ES, EX, D, F, and G for REAL data (and COMPLEX
@@ -138,4 +138,4 @@ extern template class RealOutputEditing<10>;
 extern template class RealOutputEditing<16>;
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_EDIT_OUTPUT_H_ */
+#endif /* FORTRAN_FLANG_RT_EDIT_OUTPUT_H_ */
diff --git a/FortranRuntime/lib/Runtime/emit-encoded.h b/flang-rt/lib/flang_rt/emit-encoded.h
similarity index 94%
rename from FortranRuntime/lib/Runtime/emit-encoded.h
rename to flang-rt/lib/flang_rt/emit-encoded.h
index 11163a41720795..87216e5808a286 100644
--- a/FortranRuntime/lib/Runtime/emit-encoded.h
+++ b/flang-rt/lib/flang_rt/emit-encoded.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/emit-encoded.h ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/emit-encoded.h -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Templates for emitting CHARACTER values with conversion
 
-#ifndef FORTRAN_RUNTIME_EMIT_ENCODED_H_
-#define FORTRAN_RUNTIME_EMIT_ENCODED_H_
+#ifndef FORTRAN_FLANG_RT_EMIT_ENCODED_H_
+#define FORTRAN_FLANG_RT_EMIT_ENCODED_H_
 
 #include "connection.h"
 #include "environment.h"
@@ -114,4 +114,4 @@ RT_API_ATTRS bool EmitRepeated(CONTEXT &to, char ch, std::size_t n) {
 }
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_EMIT_ENCODED_H_ */
+#endif /* FORTRAN_FLANG_RT_EMIT_ENCODED_H_ */
diff --git a/FortranRuntime/lib/Runtime/environment-default-list.h b/flang-rt/lib/flang_rt/environment-default-list.h
similarity index 100%
rename from FortranRuntime/lib/Runtime/environment-default-list.h
rename to flang-rt/lib/flang_rt/environment-default-list.h
diff --git a/FortranRuntime/lib/Runtime/environment.cpp b/flang-rt/lib/flang_rt/environment.cpp
similarity index 96%
rename from FortranRuntime/lib/Runtime/environment.cpp
rename to flang-rt/lib/flang_rt/environment.cpp
index 272914877988a5..a9447815efeeaf 100644
--- a/FortranRuntime/lib/Runtime/environment.cpp
+++ b/flang-rt/lib/flang_rt/environment.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/environment.cpp -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/environment.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -23,11 +23,11 @@ extern char **environ;
 
 namespace Fortran::runtime {
 
-#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#ifndef FLANGRT_NO_GLOBAL_VAR_DEFS
 RT_OFFLOAD_VAR_GROUP_BEGIN
 RT_VAR_ATTRS ExecutionEnvironment executionEnvironment;
 RT_OFFLOAD_VAR_GROUP_END
-#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#endif // FLANGRT_NO_GLOBAL_VAR_DEFS
 
 static void SetEnvironmentDefaults(const EnvironmentDefaultList *envDefaults) {
   if (!envDefaults) {
diff --git a/FortranRuntime/lib/Runtime/environment.h b/flang-rt/lib/flang_rt/environment.h
similarity index 91%
rename from FortranRuntime/lib/Runtime/environment.h
rename to flang-rt/lib/flang_rt/environment.h
index 7d10b3a2b934bf..125c9b39528b94 100644
--- a/FortranRuntime/lib/Runtime/environment.h
+++ b/flang-rt/lib/flang_rt/environment.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/environment.h -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/environment.h ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_ENVIRONMENT_H_
-#define FORTRAN_RUNTIME_ENVIRONMENT_H_
+#ifndef FORTRAN_FLANG_RT_ENVIRONMENT_H_
+#define FORTRAN_FLANG_RT_ENVIRONMENT_H_
 
 #include "flang/Common/decimal.h"
 #include "flang/Common/optional.h"
@@ -64,4 +64,4 @@ RT_OFFLOAD_VAR_GROUP_END
 
 } // namespace Fortran::runtime
 
-#endif /* FORTRAN_RUNTIME_ENVIRONMENT_H_ */
+#endif /* FORTRAN_FLANG_RT_ENVIRONMENT_H_ */
diff --git a/FortranRuntime/lib/Runtime/exceptions.cpp b/flang-rt/lib/flang_rt/exceptions.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/exceptions.cpp
rename to flang-rt/lib/flang_rt/exceptions.cpp
index 7739130ae2346a..9ad5fe6849b076 100644
--- a/FortranRuntime/lib/Runtime/exceptions.cpp
+++ b/flang-rt/lib/flang_rt/exceptions.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/exceptions.cpp ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/exceptions.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/execute.cpp b/flang-rt/lib/flang_rt/execute.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/execute.cpp
rename to flang-rt/lib/flang_rt/execute.cpp
index b333c61c8a59f4..d3d42a49737fed 100644
--- a/FortranRuntime/lib/Runtime/execute.cpp
+++ b/flang-rt/lib/flang_rt/execute.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/execute.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/execute.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/execute.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "environment.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "stat.h"
 #include "terminator.h"
 #include "tools.h"
diff --git a/FortranRuntime/lib/Runtime/extensions.cpp b/flang-rt/lib/flang_rt/extensions.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/extensions.cpp
rename to flang-rt/lib/flang_rt/extensions.cpp
index bb25fe6ee9d886..4cd9791cd0e5cb 100644
--- a/FortranRuntime/lib/Runtime/extensions.cpp
+++ b/flang-rt/lib/flang_rt/extensions.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/extensions.cpp ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/extensions.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,8 +10,8 @@
 // extensions that will eventually be implemented in Fortran.
 
 #include "flang/Runtime/extensions.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Runtime/command.h"
diff --git a/FortranRuntime/lib/Runtime/external-unit.cpp b/flang-rt/lib/flang_rt/external-unit.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/external-unit.cpp
rename to flang-rt/lib/flang_rt/external-unit.cpp
index f5fa2c31dafc4e..1942cc1ff4daec 100644
--- a/FortranRuntime/lib/Runtime/external-unit.cpp
+++ b/flang-rt/lib/flang_rt/external-unit.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/external-unit.cpp ---------------------------*- C++ -*-===//
+//===-- lib/flang_rt/external-unit.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/extrema.cpp b/flang-rt/lib/flang_rt/extrema.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/extrema.cpp
rename to flang-rt/lib/flang_rt/extrema.cpp
index be9da63d7bd6b8..7a230afc4190c6 100644
--- a/FortranRuntime/lib/Runtime/extrema.cpp
+++ b/flang-rt/lib/flang_rt/extrema.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/extrema.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/extrema.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/file.cpp b/flang-rt/lib/flang_rt/file.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/file.cpp
rename to flang-rt/lib/flang_rt/file.cpp
index de52dafd12df9a..d98c8afeca3514 100644
--- a/FortranRuntime/lib/Runtime/file.cpp
+++ b/flang-rt/lib/flang_rt/file.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/file.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/file.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "file.h"
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "tools.h"
 #include "flang/Runtime/magic-numbers.h"
 #include <algorithm>
diff --git a/FortranRuntime/lib/Runtime/file.h b/flang-rt/lib/flang_rt/file.h
similarity index 94%
rename from FortranRuntime/lib/Runtime/file.h
rename to flang-rt/lib/flang_rt/file.h
index 60ddf2a2741610..b4068e3dce0d14 100644
--- a/FortranRuntime/lib/Runtime/file.h
+++ b/flang-rt/lib/flang_rt/file.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/file.h --------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/file.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,10 +8,10 @@
 
 // Raw system I/O wrappers
 
-#ifndef FORTRAN_RUNTIME_FILE_H_
-#define FORTRAN_RUNTIME_FILE_H_
+#ifndef FORTRAN_FLANG_RT_FILE_H_
+#define FORTRAN_FLANG_RT_FILE_H_
 
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "io-error.h"
 #include "flang/Common/optional.h"
 #include <cinttypes>
@@ -113,4 +113,4 @@ RT_API_ATTRS bool MayWrite(const char *path);
 RT_API_ATTRS bool MayReadAndWrite(const char *path);
 RT_API_ATTRS std::int64_t SizeInBytes(const char *path);
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_FILE_H_ */
+#endif /* FORTRAN_FLANG_RT_FILE_H_ */
diff --git a/FortranRuntime/lib/Runtime/findloc.cpp b/flang-rt/lib/flang_rt/findloc.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/findloc.cpp
rename to flang-rt/lib/flang_rt/findloc.cpp
index da5fe0c0a0a467..8ee4c7c6cf7800 100644
--- a/FortranRuntime/lib/Runtime/findloc.cpp
+++ b/flang-rt/lib/flang_rt/findloc.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/findloc.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/findloc.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/format-implementation.h b/flang-rt/lib/flang_rt/format-implementation.h
similarity index 98%
rename from FortranRuntime/lib/Runtime/format-implementation.h
rename to flang-rt/lib/flang_rt/format-implementation.h
index f17f0a2cb4bfd9..9b7ad6f2ce1fc6 100644
--- a/FortranRuntime/lib/Runtime/format-implementation.h
+++ b/flang-rt/lib/flang_rt/format-implementation.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/format-implementation.h ---------------------*- C++ -*-===//
+//===-- lib/flang_rt/format-implementation.h --------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Implements out-of-line member functions of template class FormatControl
 
-#ifndef FORTRAN_RUNTIME_FORMAT_IMPLEMENTATION_H_
-#define FORTRAN_RUNTIME_FORMAT_IMPLEMENTATION_H_
+#ifndef FORTRAN_FLANG_RT_FORMAT_IMPLEMENTATION_H_
+#define FORTRAN_FLANG_RT_FORMAT_IMPLEMENTATION_H_
 
 #include "emit-encoded.h"
 #include "format.h"
@@ -601,4 +601,4 @@ RT_API_ATTRS void FormatControl<CONTEXT>::Finish(Context &context) {
   }
 }
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_FORMAT_IMPLEMENTATION_H_ */
+#endif /* FORTRAN_FLANG_RT_FORMAT_IMPLEMENTATION_H_ */
diff --git a/FortranRuntime/lib/Runtime/format.cpp b/flang-rt/lib/flang_rt/format.cpp
similarity index 93%
rename from FortranRuntime/lib/Runtime/format.cpp
rename to flang-rt/lib/flang_rt/format.cpp
index 73a61f785c23b8..aedf04b8a40a1b 100644
--- a/FortranRuntime/lib/Runtime/format.cpp
+++ b/flang-rt/lib/flang_rt/format.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/format.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/format.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/format.h b/flang-rt/lib/flang_rt/format.h
similarity index 97%
rename from FortranRuntime/lib/Runtime/format.h
rename to flang-rt/lib/flang_rt/format.h
index 098a251a04d568..b41eec9564baaa 100644
--- a/FortranRuntime/lib/Runtime/format.h
+++ b/flang-rt/lib/flang_rt/format.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/format.h ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/format.h -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // FORMAT string processing
 
-#ifndef FORTRAN_RUNTIME_FORMAT_H_
-#define FORTRAN_RUNTIME_FORMAT_H_
+#ifndef FORTRAN_FLANG_RT_FORMAT_H_
+#define FORTRAN_FLANG_RT_FORMAT_H_
 
 #include "environment.h"
 #include "io-error.h"
@@ -201,4 +201,4 @@ template <typename CONTEXT> class FormatControl {
   Iteration stack_[maxMaxHeight];
 };
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_FORMAT_H_ */
+#endif /* FORTRAN_FLANG_RT_FORMAT_H_ */
diff --git a/FortranRuntime/lib/Runtime/inquiry.cpp b/flang-rt/lib/flang_rt/inquiry.cpp
similarity index 96%
rename from FortranRuntime/lib/Runtime/inquiry.cpp
rename to flang-rt/lib/flang_rt/inquiry.cpp
index c24492754b4f43..b29ab4ee3c6663 100644
--- a/FortranRuntime/lib/Runtime/inquiry.cpp
+++ b/flang-rt/lib/flang_rt/inquiry.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/inquiry.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/inquiry.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,8 +10,8 @@
 // inquire about shape information of arrays -- LBOUND and SIZE.
 
 #include "flang/Runtime/inquiry.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "copy.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include <algorithm>
diff --git a/FortranRuntime/lib/Runtime/internal-unit.cpp b/flang-rt/lib/flang_rt/internal-unit.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/internal-unit.cpp
rename to flang-rt/lib/flang_rt/internal-unit.cpp
index 4494de9dddc1a1..7775ded1e86d57 100644
--- a/FortranRuntime/lib/Runtime/internal-unit.cpp
+++ b/flang-rt/lib/flang_rt/internal-unit.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/internal-unit.cpp ---------------------------*- C++ -*-===//
+//===-- lib/flang_rt/internal-unit.cpp --------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "internal-unit.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "io-error.h"
 #include "flang/Runtime/freestanding-tools.h"
 #include <algorithm>
diff --git a/FortranRuntime/lib/Runtime/internal-unit.h b/flang-rt/lib/flang_rt/internal-unit.h
similarity index 89%
rename from FortranRuntime/lib/Runtime/internal-unit.h
rename to flang-rt/lib/flang_rt/internal-unit.h
index 7579016f14646d..2f7d0220b84b37 100644
--- a/FortranRuntime/lib/Runtime/internal-unit.h
+++ b/flang-rt/lib/flang_rt/internal-unit.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/internal-unit.h -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/internal-unit.h ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,11 +8,11 @@
 
 // Fortran internal I/O "units"
 
-#ifndef FORTRAN_RUNTIME_INTERNAL_UNIT_H_
-#define FORTRAN_RUNTIME_INTERNAL_UNIT_H_
+#ifndef FORTRAN_FLANG_RT_INTERNAL_UNIT_H_
+#define FORTRAN_FLANG_RT_INTERNAL_UNIT_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "connection.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include <cinttypes>
 #include <type_traits>
 
@@ -56,4 +56,4 @@ template <Direction DIR> class InternalDescriptorUnit : public ConnectionState {
 extern template class InternalDescriptorUnit<Direction::Output>;
 extern template class InternalDescriptorUnit<Direction::Input>;
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_INTERNAL_UNIT_H_ */
+#endif /* FORTRAN_FLANG_RT_INTERNAL_UNIT_H_ */
diff --git a/FortranRuntime/lib/Runtime/io-api-common.h b/flang-rt/lib/flang_rt/io-api-common.h
similarity index 92%
rename from FortranRuntime/lib/Runtime/io-api-common.h
rename to flang-rt/lib/flang_rt/io-api-common.h
index fed1d11d6ce6a6..5ff1b57c73cda6 100644
--- a/FortranRuntime/lib/Runtime/io-api-common.h
+++ b/flang-rt/lib/flang_rt/io-api-common.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/io-api-common.h -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/io-api-common.h ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,10 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_IO_API_COMMON_H_
-#define FORTRAN_RUNTIME_IO_API_COMMON_H_
+#ifndef FORTRAN_FLANG_RT_IO_API_COMMON_H_
+#define FORTRAN_FLANG_RT_IO_API_COMMON_H_
 
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "io-stmt.h"
 #include "terminator.h"
 #include "unit.h"
@@ -94,4 +94,4 @@ RT_API_ATTRS Cookie BeginExternalListIO(
 }
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_IO_API_COMMON_H_ */
+#endif /* FORTRAN_FLANG_RT_IO_API_COMMON_H_ */
diff --git a/FortranRuntime/lib/Runtime/io-api-minimal.cpp b/flang-rt/lib/flang_rt/io-api-minimal.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/io-api-minimal.cpp
rename to flang-rt/lib/flang_rt/io-api-minimal.cpp
index 8cde2333804572..92524430650126 100644
--- a/FortranRuntime/lib/Runtime/io-api-minimal.cpp
+++ b/flang-rt/lib/flang_rt/io-api-minimal.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/io-api-minimal.cpp --------------------------*- C++ -*-===//
+//===-- lib/flang_rt/io-api-minimal.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,8 +9,8 @@
 // Implements the subset of the I/O statement API needed for basic
 // list-directed output (PRINT *) of intrinsic types.
 
-#include "FortranRuntime/Runtime/io-api-funcs.h"
 #include "edit-output.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "format.h"
 #include "io-api-common.h"
 #include "io-stmt.h"
diff --git a/FortranRuntime/lib/Runtime/io-api.cpp b/flang-rt/lib/flang_rt/io-api.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/io-api.cpp
rename to flang-rt/lib/flang_rt/io-api.cpp
index fa95d68a004b51..0de1e24f71dac5 100644
--- a/FortranRuntime/lib/Runtime/io-api.cpp
+++ b/flang-rt/lib/flang_rt/io-api.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/io-api.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/io-api.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -13,13 +13,13 @@
 // OutputReal{32,64}, OutputComplex{32,64}, OutputAscii, & EndIoStatement()
 // are in runtime/io-api-minimal.cpp.
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
-#include "FortranRuntime/Runtime/memory.h"
 #include "descriptor-io.h"
 #include "edit-input.h"
 #include "edit-output.h"
 #include "environment.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "format.h"
 #include "io-api-common.h"
 #include "io-stmt.h"
diff --git a/FortranRuntime/lib/Runtime/io-error.cpp b/flang-rt/lib/flang_rt/io-error.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/io-error.cpp
rename to flang-rt/lib/flang_rt/io-error.cpp
index 053667462058de..215c839d98cc35 100644
--- a/FortranRuntime/lib/Runtime/io-error.cpp
+++ b/flang-rt/lib/flang_rt/io-error.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/io-error.cpp --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/io-error.cpp -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/io-error.h b/flang-rt/lib/flang_rt/io-error.h
similarity index 90%
rename from FortranRuntime/lib/Runtime/io-error.h
rename to flang-rt/lib/flang_rt/io-error.h
index e2018cc2ea0ab1..7798d0830a1323 100644
--- a/FortranRuntime/lib/Runtime/io-error.h
+++ b/flang-rt/lib/flang_rt/io-error.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/io-error.h ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/io-error.h ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -12,11 +12,11 @@
 // IOSTAT error codes are raw errno values augmented with values for
 // Fortran-specific errors.
 
-#ifndef FORTRAN_RUNTIME_IO_ERROR_H_
-#define FORTRAN_RUNTIME_IO_ERROR_H_
+#ifndef FORTRAN_FLANG_RT_IO_ERROR_H_
+#define FORTRAN_FLANG_RT_IO_ERROR_H_
 
-#include "FortranRuntime/Runtime/iostat-funcs.h"
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/iostat-funcs.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "terminator.h"
 #include <cinttypes>
 
@@ -78,4 +78,4 @@ class IoErrorHandler : public Terminator {
 };
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_IO_ERROR_H_ */
+#endif /* FORTRAN_FLANG_RT_IO_ERROR_H_ */
diff --git a/FortranRuntime/lib/Runtime/io-stmt.cpp b/flang-rt/lib/flang_rt/io-stmt.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/io-stmt.cpp
rename to flang-rt/lib/flang_rt/io-stmt.cpp
index fe02e221671665..7c243a8c934a7a 100644
--- a/FortranRuntime/lib/Runtime/io-stmt.cpp
+++ b/flang-rt/lib/flang_rt/io-stmt.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/io-stmt.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/io-stmt.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "io-stmt.h"
-#include "FortranRuntime/Runtime/memory.h"
 #include "connection.h"
 #include "emit-encoded.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "format.h"
 #include "tools.h"
 #include "unit.h"
diff --git a/FortranRuntime/lib/Runtime/io-stmt.h b/flang-rt/lib/flang_rt/io-stmt.h
similarity index 99%
rename from FortranRuntime/lib/Runtime/io-stmt.h
rename to flang-rt/lib/flang_rt/io-stmt.h
index 21746ff1966218..78bc42502be687 100644
--- a/FortranRuntime/lib/Runtime/io-stmt.h
+++ b/flang-rt/lib/flang_rt/io-stmt.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/io-stmt.h -----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/io-stmt.h ----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,13 +8,13 @@
 
 // Representations of the state of an I/O statement in progress
 
-#ifndef FORTRAN_RUNTIME_IO_STMT_H_
-#define FORTRAN_RUNTIME_IO_STMT_H_
+#ifndef FORTRAN_FLANG_RT_IO_STMT_H_
+#define FORTRAN_FLANG_RT_IO_STMT_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
 #include "connection.h"
 #include "file.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "format.h"
 #include "internal-unit.h"
 #include "io-error.h"
@@ -789,4 +789,4 @@ class ErroneousIoStatementState : public IoStatementBase {
 };
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_IO_STMT_H_ */
+#endif /* FORTRAN_FLANG_RT_IO_STMT_H_ */
diff --git a/FortranRuntime/lib/Runtime/iostat.cpp b/flang-rt/lib/flang_rt/iostat.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/iostat.cpp
rename to flang-rt/lib/flang_rt/iostat.cpp
index 8d769a09252fd6..39f4474dcf7229 100644
--- a/FortranRuntime/lib/Runtime/iostat.cpp
+++ b/flang-rt/lib/flang_rt/iostat.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/iostat.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/iostat.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/iostat-funcs.h"
+#include "flang-rt/flang_rt/iostat-funcs.h"
 
 namespace Fortran::runtime::io {
 RT_OFFLOAD_API_GROUP_BEGIN
diff --git a/FortranRuntime/lib/Runtime/lock.h b/flang-rt/lib/flang_rt/lock.h
similarity index 94%
rename from FortranRuntime/lib/Runtime/lock.h
rename to flang-rt/lib/flang_rt/lock.h
index 69ff6403736dae..955059a711c47d 100644
--- a/FortranRuntime/lib/Runtime/lock.h
+++ b/flang-rt/lib/flang_rt/lock.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/lock.h --------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/lock.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Wraps a mutex
 
-#ifndef FORTRAN_RUNTIME_LOCK_H_
-#define FORTRAN_RUNTIME_LOCK_H_
+#ifndef FORTRAN_FLANG_RT_LOCK_H_
+#define FORTRAN_FLANG_RT_LOCK_H_
 
 #include "terminator.h"
 #include "tools.h"
@@ -113,4 +113,4 @@ class CriticalSection {
 };
 } // namespace Fortran::runtime
 
-#endif /* FORTRAN_RUNTIME_LOCK_H_ */
+#endif /* FORTRAN_FLANG_RT_LOCK_H_ */
diff --git a/FortranRuntime/lib/Runtime/main.cpp b/flang-rt/lib/flang_rt/main.cpp
similarity index 95%
rename from FortranRuntime/lib/Runtime/main.cpp
rename to flang-rt/lib/flang_rt/main.cpp
index 3fe985e524548d..71ed7f8319f60f 100644
--- a/FortranRuntime/lib/Runtime/main.cpp
+++ b/flang-rt/lib/flang_rt/main.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/main.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/main.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/matmul-transpose.cpp b/flang-rt/lib/flang_rt/matmul-transpose.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/matmul-transpose.cpp
rename to flang-rt/lib/flang_rt/matmul-transpose.cpp
index ec5388e3fca793..2c7c4a89117f04 100644
--- a/FortranRuntime/lib/Runtime/matmul-transpose.cpp
+++ b/flang-rt/lib/flang_rt/matmul-transpose.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/matmul-transpose.cpp ------------------------*- C++ -*-===//
+//===-- lib/flang_rt/matmul-transpose.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -21,7 +21,7 @@
 // to use the faster BLAS routines.
 
 #include "flang/Runtime/matmul-transpose.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Common/optional.h"
diff --git a/FortranRuntime/lib/Runtime/matmul.cpp b/flang-rt/lib/flang_rt/matmul.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/matmul.cpp
rename to flang-rt/lib/flang_rt/matmul.cpp
index 01be7f7c75bc45..8157911f34fd38 100644
--- a/FortranRuntime/lib/Runtime/matmul.cpp
+++ b/flang-rt/lib/flang_rt/matmul.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/matmul.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/matmul.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -20,7 +20,7 @@
 // Places where BLAS routines could be called are marked as TODO items.
 
 #include "flang/Runtime/matmul.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Common/optional.h"
diff --git a/FortranRuntime/lib/Runtime/memory.cpp b/flang-rt/lib/flang_rt/memory.cpp
similarity index 92%
rename from FortranRuntime/lib/Runtime/memory.cpp
rename to flang-rt/lib/flang_rt/memory.cpp
index a4cebf7edc6c64..66aa5be0cddc60 100644
--- a/FortranRuntime/lib/Runtime/memory.cpp
+++ b/flang-rt/lib/flang_rt/memory.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/memory.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/memory.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Runtime/freestanding-tools.h"
diff --git a/FortranRuntime/lib/Runtime/misc-intrinsic.cpp b/flang-rt/lib/flang_rt/misc-intrinsic.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/misc-intrinsic.cpp
rename to flang-rt/lib/flang_rt/misc-intrinsic.cpp
index 91a3b136e009a5..00098c5b4e20b0 100644
--- a/FortranRuntime/lib/Runtime/misc-intrinsic.cpp
+++ b/flang-rt/lib/flang_rt/misc-intrinsic.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/misc-intrinsic.cpp --------------------------*- C++ -*-===//
+//===-- lib/flang_rt/misc-intrinsic.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/misc-intrinsic.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Common/optional.h"
diff --git a/FortranRuntime/lib/Runtime/namelist.cpp b/flang-rt/lib/flang_rt/namelist.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/namelist.cpp
rename to flang-rt/lib/flang_rt/namelist.cpp
index 46036549bcd316..92dbd33b7f9609 100644
--- a/FortranRuntime/lib/Runtime/namelist.cpp
+++ b/flang-rt/lib/flang_rt/namelist.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/namelist.cpp --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/namelist.cpp -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "namelist.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
 #include "descriptor-io.h"
 #include "emit-encoded.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "io-stmt.h"
 #include <algorithm>
 #include <cstring>
diff --git a/FortranRuntime/lib/Runtime/namelist.h b/flang-rt/lib/flang_rt/namelist.h
similarity index 91%
rename from FortranRuntime/lib/Runtime/namelist.h
rename to flang-rt/lib/flang_rt/namelist.h
index 04432f8a08cb97..519ec5dd2ddbc5 100644
--- a/FortranRuntime/lib/Runtime/namelist.h
+++ b/flang-rt/lib/flang_rt/namelist.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/namelist.h ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/namelist.h ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Defines the data structure used for NAMELIST I/O
 
-#ifndef FORTRAN_RUNTIME_NAMELIST_H_
-#define FORTRAN_RUNTIME_NAMELIST_H_
+#ifndef FORTRAN_FLANG_RT_NAMELIST_H_
+#define FORTRAN_FLANG_RT_NAMELIST_H_
 
 #include "non-tbp-dio.h"
 #include "flang/Common/api-attrs.h"
@@ -51,4 +51,4 @@ class NamelistGroup {
 RT_API_ATTRS bool IsNamelistNameOrSlash(IoStatementState &);
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_NAMELIST_H_ */
+#endif /* FORTRAN_FLANG_RT_NAMELIST_H_ */
diff --git a/FortranRuntime/lib/Runtime/non-tbp-dio.cpp b/flang-rt/lib/flang_rt/non-tbp-dio.cpp
similarity index 93%
rename from FortranRuntime/lib/Runtime/non-tbp-dio.cpp
rename to flang-rt/lib/flang_rt/non-tbp-dio.cpp
index 9fa04397bc9610..3aade68cbb6d3e 100644
--- a/FortranRuntime/lib/Runtime/non-tbp-dio.cpp
+++ b/flang-rt/lib/flang_rt/non-tbp-dio.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/non-tbp-dio.cpp -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/non-tbp-dio.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/non-tbp-dio.h b/flang-rt/lib/flang_rt/non-tbp-dio.h
similarity index 91%
rename from FortranRuntime/lib/Runtime/non-tbp-dio.h
rename to flang-rt/lib/flang_rt/non-tbp-dio.h
index 426d5a92fd37d4..dfc96603a8eb1c 100644
--- a/FortranRuntime/lib/Runtime/non-tbp-dio.h
+++ b/flang-rt/lib/flang_rt/non-tbp-dio.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/non-tbp-dio.h -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/non-tbp-dio.h ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -19,8 +19,8 @@
 // a containing scope has become inaccessible in a nested scope due
 // to the use of "IMPORT, NONE" or "IMPORT, ONLY:".
 
-#ifndef FORTRAN_RUNTIME_NON_TBP_DIO_H_
-#define FORTRAN_RUNTIME_NON_TBP_DIO_H_
+#ifndef FORTRAN_FLANG_RT_NON_TBP_DIO_H_
+#define FORTRAN_FLANG_RT_NON_TBP_DIO_H_
 
 #include "flang/Common/Fortran-consts.h"
 #include "flang/Common/api-attrs.h"
@@ -53,4 +53,4 @@ struct NonTbpDefinedIoTable {
 };
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_NON_TBP_DIO_H_ */
+#endif /* FORTRAN_FLANG_RT_NON_TBP_DIO_H_ */
diff --git a/FortranRuntime/lib/Runtime/numeric-templates.h b/flang-rt/lib/flang_rt/numeric-templates.h
similarity index 98%
rename from FortranRuntime/lib/Runtime/numeric-templates.h
rename to flang-rt/lib/flang_rt/numeric-templates.h
index 159b8b0b9579ad..0471b89f9153ad 100644
--- a/FortranRuntime/lib/Runtime/numeric-templates.h
+++ b/flang-rt/lib/flang_rt/numeric-templates.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/numeric-templates.h -------------------------*- C++ -*-===//
+//===-- lib/flang_rt/numeric-templates.h ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -15,8 +15,8 @@
 // for the data type corresponding to CppTypeFor<TypeCategory::Real, 16>
 // on the target.
 
-#ifndef FORTRAN_RUNTIME_NUMERIC_TEMPLATES_H_
-#define FORTRAN_RUNTIME_NUMERIC_TEMPLATES_H_
+#ifndef FORTRAN_FLANG_RT_NUMERIC_TEMPLATES_H_
+#define FORTRAN_FLANG_RT_NUMERIC_TEMPLATES_H_
 
 #include "terminator.h"
 #include "tools.h"
@@ -465,4 +465,4 @@ template <typename T> inline RT_API_ATTRS T ErfcScaled(T arg) {
 
 } // namespace Fortran::runtime
 
-#endif /* FORTRAN_RUNTIME_NUMERIC_TEMPLATES_H_ */
+#endif /* FORTRAN_FLANG_RT_NUMERIC_TEMPLATES_H_ */
diff --git a/FortranRuntime/lib/Runtime/numeric.cpp b/flang-rt/lib/flang_rt/numeric.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/numeric.cpp
rename to flang-rt/lib/flang_rt/numeric.cpp
index b0f68a7fc81d29..4c2c0394ede188 100644
--- a/FortranRuntime/lib/Runtime/numeric.cpp
+++ b/flang-rt/lib/flang_rt/numeric.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/numeric.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/numeric.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/pointer.cpp b/flang-rt/lib/flang_rt/pointer.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/pointer.cpp
rename to flang-rt/lib/flang_rt/pointer.cpp
index fba9e639fa37a8..7479cd780709fa 100644
--- a/FortranRuntime/lib/Runtime/pointer.cpp
+++ b/flang-rt/lib/flang_rt/pointer.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/pointer.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/pointer.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/product.cpp b/flang-rt/lib/flang_rt/product.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/product.cpp
rename to flang-rt/lib/flang_rt/product.cpp
index e4a6e81bd0c508..cd0c4e9440ceb3 100644
--- a/FortranRuntime/lib/Runtime/product.cpp
+++ b/flang-rt/lib/flang_rt/product.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/product.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/product.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/pseudo-unit.cpp b/flang-rt/lib/flang_rt/pseudo-unit.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/pseudo-unit.cpp
rename to flang-rt/lib/flang_rt/pseudo-unit.cpp
index 62c6b1df5071c7..9ce39ca9307c9c 100644
--- a/FortranRuntime/lib/Runtime/pseudo-unit.cpp
+++ b/flang-rt/lib/flang_rt/pseudo-unit.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/pseudo-unit.cpp -----------------------------*- C++ -*-===//
+//===-- lib/flang_rt/pseudo-unit.cpp ----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/ragged.cpp b/flang-rt/lib/flang_rt/ragged.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/ragged.cpp
rename to flang-rt/lib/flang_rt/ragged.cpp
index 681a800e29dca7..df6469e9c5ba27 100644
--- a/FortranRuntime/lib/Runtime/ragged.cpp
+++ b/flang-rt/lib/flang_rt/ragged.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/ragged.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/ragged.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/random-templates.h b/flang-rt/lib/flang_rt/random-templates.h
similarity index 91%
rename from FortranRuntime/lib/Runtime/random-templates.h
rename to flang-rt/lib/flang_rt/random-templates.h
index 9faa9c7cfa7002..475c972a823226 100644
--- a/FortranRuntime/lib/Runtime/random-templates.h
+++ b/flang-rt/lib/flang_rt/random-templates.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/random-templates.h --------------------------*- C++ -*-===//
+//===-- lib/flang_rt/random-templates.h -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,10 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_RANDOM_TEMPLATES_H_
-#define FORTRAN_RUNTIME_RANDOM_TEMPLATES_H_
+#ifndef FORTRAN_FLANG_RT_RANDOM_TEMPLATES_H_
+#define FORTRAN_FLANG_RT_RANDOM_TEMPLATES_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "lock.h"
 #include "numeric-templates.h"
 #include "flang/Common/optional.h"
@@ -85,4 +85,4 @@ inline void Generate(const Descriptor &harvest) {
 
 } // namespace Fortran::runtime::random
 
-#endif /* FORTRAN_RUNTIME_RANDOM_TEMPLATES_H_ */
+#endif /* FORTRAN_FLANG_RT_RANDOM_TEMPLATES_H_ */
diff --git a/FortranRuntime/lib/Runtime/random.cpp b/flang-rt/lib/flang_rt/random.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/random.cpp
rename to flang-rt/lib/flang_rt/random.cpp
index 911b59b508eb4f..9922ae87b084a8 100644
--- a/FortranRuntime/lib/Runtime/random.cpp
+++ b/flang-rt/lib/flang_rt/random.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/random.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/random.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,7 +10,7 @@
 // RANDOM_SEED.
 
 #include "flang/Runtime/random.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "lock.h"
 #include "random-templates.h"
 #include "terminator.h"
diff --git a/FortranRuntime/lib/Runtime/reduce.cpp b/flang-rt/lib/flang_rt/reduce.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/reduce.cpp
rename to flang-rt/lib/flang_rt/reduce.cpp
index a020ffef6fe6a5..6997d4c63065b9 100644
--- a/FortranRuntime/lib/Runtime/reduce.cpp
+++ b/flang-rt/lib/flang_rt/reduce.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/reduce.cpp ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/reduce.cpp ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,7 +9,7 @@
 // REDUCE() implementation
 
 #include "flang/Runtime/reduce.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "reduction-templates.h"
 #include "terminator.h"
 #include "tools.h"
diff --git a/FortranRuntime/lib/Runtime/reduction-templates.h b/flang-rt/lib/flang_rt/reduction-templates.h
similarity index 98%
rename from FortranRuntime/lib/Runtime/reduction-templates.h
rename to flang-rt/lib/flang_rt/reduction-templates.h
index 714584ec613ba3..774b6f3c99850f 100644
--- a/FortranRuntime/lib/Runtime/reduction-templates.h
+++ b/flang-rt/lib/flang_rt/reduction-templates.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/reduction-templates.h -----------------------*- C++ -*-===//
+//===-- lib/flang_rt/reduction-templates.h ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -18,10 +18,10 @@
 // * Character-valued reductions (MAXVAL & MINVAL) return arbitrary
 //   length results, dynamically allocated in a caller-supplied descriptor
 
-#ifndef FORTRAN_RUNTIME_REDUCTION_TEMPLATES_H_
-#define FORTRAN_RUNTIME_REDUCTION_TEMPLATES_H_
+#ifndef FORTRAN_FLANG_RT_REDUCTION_TEMPLATES_H_
+#define FORTRAN_FLANG_RT_REDUCTION_TEMPLATES_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "numeric-templates.h"
 #include "terminator.h"
 #include "tools.h"
@@ -412,4 +412,4 @@ template <int KIND> struct Norm2Helper {
 };
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_REDUCTION_TEMPLATES_H_ */
+#endif /* FORTRAN_FLANG_RT_REDUCTION_TEMPLATES_H_ */
diff --git a/FortranRuntime/lib/Runtime/reduction.cpp b/flang-rt/lib/flang_rt/reduction.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/reduction.cpp
rename to flang-rt/lib/flang_rt/reduction.cpp
index 21930fee07ead7..f9d5f442e8928f 100644
--- a/FortranRuntime/lib/Runtime/reduction.cpp
+++ b/flang-rt/lib/flang_rt/reduction.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/reduction.cpp -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/reduction.cpp ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -14,7 +14,7 @@
 // NORM2, MAXLOC, MINLOC, MAXVAL, and MINVAL are in extrema.cpp.
 
 #include "flang/Runtime/reduction.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "reduction-templates.h"
 #include <cinttypes>
 
diff --git a/FortranRuntime/lib/Runtime/stack.h b/flang-rt/lib/flang_rt/stack.h
similarity index 94%
rename from FortranRuntime/lib/Runtime/stack.h
rename to flang-rt/lib/flang_rt/stack.h
index 36e2d0a103a887..4c1ab4e85ed71f 100644
--- a/FortranRuntime/lib/Runtime/stack.h
+++ b/flang-rt/lib/flang_rt/stack.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stack.h -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stack.h ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,10 +10,10 @@
 // It is a list based stack with dynamic allocation/deallocation
 // of the list nodes.
 
-#ifndef FORTRAN_RUNTIME_STACK_H_
-#define FORTRAN_RUNTIME_STACK_H_
+#ifndef FORTRAN_FLANG_RT_STACK_H_
+#define FORTRAN_FLANG_RT_STACK_H_
 
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "terminator.h"
 
 namespace Fortran::runtime {
@@ -133,4 +133,4 @@ template <typename T, unsigned N = 0> class Stack : public StackStorage<T, N> {
   Terminator &terminator_;
 };
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_STACK_H_ */
+#endif /* FORTRAN_FLANG_RT_STACK_H_ */
diff --git a/FortranRuntime/lib/Runtime/stat.cpp b/flang-rt/lib/flang_rt/stat.cpp
similarity index 96%
rename from FortranRuntime/lib/Runtime/stat.cpp
rename to flang-rt/lib/flang_rt/stat.cpp
index 1af6c43102518b..77eefe3d1ac518 100644
--- a/FortranRuntime/lib/Runtime/stat.cpp
+++ b/flang-rt/lib/flang_rt/stat.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stat.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stat.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "stat.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 
diff --git a/FortranRuntime/lib/Runtime/stat.h b/flang-rt/lib/flang_rt/stat.h
similarity index 93%
rename from FortranRuntime/lib/Runtime/stat.h
rename to flang-rt/lib/flang_rt/stat.h
index eccd69024d726b..dbab381001d7d8 100644
--- a/FortranRuntime/lib/Runtime/stat.h
+++ b/flang-rt/lib/flang_rt/stat.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stat.h --------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stat.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,8 +9,8 @@
 // Defines the values returned by the runtime for STAT= specifiers
 // on executable statements.
 
-#ifndef FORTRAN_RUNTIME_STAT_H_
-#define FORTRAN_RUNTIME_STAT_H_
+#ifndef FORTRAN_FLANG_RT_STAT_H_
+#define FORTRAN_FLANG_RT_STAT_H_
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Common/api-attrs.h"
 #include "flang/Runtime/magic-numbers.h"
@@ -60,4 +60,4 @@ RT_API_ATTRS int ToErrmsg(const Descriptor *errmsg, int stat); // returns stat
 RT_API_ATTRS int ReturnError(Terminator &, int stat,
     const Descriptor *errmsg = nullptr, bool hasStat = false);
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_STAT_H_ */
+#endif /* FORTRAN_FLANG_RT_STAT_H_ */
diff --git a/FortranRuntime/lib/Runtime/stop.cpp b/flang-rt/lib/flang_rt/stop.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/stop.cpp
rename to flang-rt/lib/flang_rt/stop.cpp
index 8465a53168e551..ea50d1ba4747ff 100644
--- a/FortranRuntime/lib/Runtime/stop.cpp
+++ b/flang-rt/lib/flang_rt/stop.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/stop.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/stop.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/sum.cpp b/flang-rt/lib/flang_rt/sum.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/sum.cpp
rename to flang-rt/lib/flang_rt/sum.cpp
index 64982b9fd53690..3c225efe8a2788 100644
--- a/FortranRuntime/lib/Runtime/sum.cpp
+++ b/flang-rt/lib/flang_rt/sum.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/sum.cpp -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/sum.cpp ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/support.cpp b/flang-rt/lib/flang_rt/support.cpp
similarity index 93%
rename from FortranRuntime/lib/Runtime/support.cpp
rename to flang-rt/lib/flang_rt/support.cpp
index 798d502ba248e2..436ae6f87ae692 100644
--- a/FortranRuntime/lib/Runtime/support.cpp
+++ b/flang-rt/lib/flang_rt/support.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/support.cpp ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/support.cpp --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/support.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "ISO_Fortran_util.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "type-info.h"
 
 namespace Fortran::runtime {
diff --git a/FortranRuntime/lib/Runtime/temporary-stack.cpp b/flang-rt/lib/flang_rt/temporary-stack.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/temporary-stack.cpp
rename to flang-rt/lib/flang_rt/temporary-stack.cpp
index d8ff08e51cc211..f566e6d8a086ff 100644
--- a/FortranRuntime/lib/Runtime/temporary-stack.cpp
+++ b/flang-rt/lib/flang_rt/temporary-stack.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/temporary-stack.cpp -------------------------*- C++ -*-===//
+//===-- lib/flang_rt/temporary-stack.cpp ------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,8 +10,8 @@
 // temporaries. For use in HLFIR lowering.
 
 #include "flang/Runtime/temporary-stack.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "terminator.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Runtime/assign.h"
diff --git a/FortranRuntime/lib/Runtime/terminator.cpp b/flang-rt/lib/flang_rt/terminator.cpp
similarity index 97%
rename from FortranRuntime/lib/Runtime/terminator.cpp
rename to flang-rt/lib/flang_rt/terminator.cpp
index 4146e28235511f..2e8d895a9025a6 100644
--- a/FortranRuntime/lib/Runtime/terminator.cpp
+++ b/flang-rt/lib/flang_rt/terminator.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/terminator.cpp ------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/terminator.cpp -----------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/terminator.h b/flang-rt/lib/flang_rt/terminator.h
similarity index 95%
rename from FortranRuntime/lib/Runtime/terminator.h
rename to flang-rt/lib/flang_rt/terminator.h
index f475658b0eab3d..61c6452a282d12 100644
--- a/FortranRuntime/lib/Runtime/terminator.h
+++ b/flang-rt/lib/flang_rt/terminator.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/terminator.h --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/terminator.h -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,8 +8,8 @@
 
 // Termination of the image
 
-#ifndef FORTRAN_RUNTIME_TERMINATOR_H_
-#define FORTRAN_RUNTIME_TERMINATOR_H_
+#ifndef FORTRAN_FLANG_RT_TERMINATOR_H_
+#define FORTRAN_FLANG_RT_TERMINATOR_H_
 
 #include "flang/Common/api-attrs.h"
 #include <cstdarg>
@@ -121,4 +121,4 @@ namespace Fortran::runtime::io {
 RT_API_ATTRS void FlushOutputOnCrash(const Terminator &);
 }
 
-#endif /* FORTRAN_RUNTIME_TERMINATOR_H_ */
+#endif /* FORTRAN_FLANG_RT_TERMINATOR_H_ */
diff --git a/FortranRuntime/lib/Runtime/time-intrinsic.cpp b/flang-rt/lib/flang_rt/time-intrinsic.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/time-intrinsic.cpp
rename to flang-rt/lib/flang_rt/time-intrinsic.cpp
index 15c42077c0afd5..6e2befbc30e9fa 100644
--- a/FortranRuntime/lib/Runtime/time-intrinsic.cpp
+++ b/flang-rt/lib/flang_rt/time-intrinsic.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/time-intrinsic.cpp --------------------------*- C++ -*-===//
+//===-- lib/flang_rt/time-intrinsic.cpp -------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,7 +9,7 @@
 // Implements time-related intrinsic subroutines.
 
 #include "flang/Runtime/time-intrinsic.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Runtime/cpp-type.h"
@@ -62,7 +62,7 @@ template <typename Unused = void> double GetCpuTime(fallback_implementation) {
 
 #if defined __MINGW32__
 // clock_gettime is implemented in the pthread library for MinGW.
-// Using it here would mean that all programs that link libFortranRuntime are
+// Using it here would mean that all programs that link libflang_rt are
 // required to also link to pthread. Instead, don't use the function.
 #undef CLOCKID_CPU_TIME
 #undef CLOCKID_ELAPSED_TIME
diff --git a/FortranRuntime/lib/Runtime/tools.cpp b/flang-rt/lib/flang_rt/tools.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/tools.cpp
rename to flang-rt/lib/flang_rt/tools.cpp
index d5c113a31fc501..228b781b207ddd 100644
--- a/FortranRuntime/lib/Runtime/tools.cpp
+++ b/flang-rt/lib/flang_rt/tools.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/tools.cpp -----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/tools.cpp ----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/tools.h b/flang-rt/lib/flang_rt/tools.h
similarity index 98%
rename from FortranRuntime/lib/Runtime/tools.h
rename to flang-rt/lib/flang_rt/tools.h
index 332ffac77f2595..9880d0e93f5a82 100644
--- a/FortranRuntime/lib/Runtime/tools.h
+++ b/flang-rt/lib/flang_rt/tools.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/tools.h -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/tools.h ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,11 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_TOOLS_H_
-#define FORTRAN_RUNTIME_TOOLS_H_
+#ifndef FORTRAN_FLANG_RT_TOOLS_H_
+#define FORTRAN_FLANG_RT_TOOLS_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "stat.h"
 #include "terminator.h"
 #include "flang/Common/optional.h"
@@ -535,4 +535,4 @@ RT_API_ATTRS void CreatePartialReductionResult(Descriptor &result,
     const char *intrinsic, TypeCode);
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_TOOLS_H_ */
+#endif /* FORTRAN_FLANG_RT_TOOLS_H_ */
diff --git a/FortranRuntime/lib/Runtime/transformational.cpp b/flang-rt/lib/flang_rt/transformational.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/transformational.cpp
rename to flang-rt/lib/flang_rt/transformational.cpp
index 28dd02a28036de..f21c63fbfd7a1b 100644
--- a/FortranRuntime/lib/Runtime/transformational.cpp
+++ b/flang-rt/lib/flang_rt/transformational.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/transformational.cpp ------------------------*- C++ -*-===//
+//===-- lib/flang_rt/transformational.cpp -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -17,8 +17,8 @@
 // of the standard but it more likely to conform with its intent.
 
 #include "flang/Runtime/transformational.h"
-#include "FortranRuntime/Runtime/descriptor.h"
 #include "copy.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "tools.h"
 #include "flang/Common/float128.h"
diff --git a/FortranRuntime/lib/Runtime/type-code.cpp b/flang-rt/lib/flang_rt/type-code.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/type-code.cpp
rename to flang-rt/lib/flang_rt/type-code.cpp
index 16f5497bc7a709..96fabf7ec7698f 100644
--- a/FortranRuntime/lib/Runtime/type-code.cpp
+++ b/flang-rt/lib/flang_rt/type-code.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/type-code.cpp -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/type-code.cpp ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include <cstdint>
 
 namespace Fortran::runtime {
diff --git a/FortranRuntime/lib/Runtime/type-info.cpp b/flang-rt/lib/flang_rt/type-info.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/type-info.cpp
rename to flang-rt/lib/flang_rt/type-info.cpp
index 19e9211fc063f4..031721833ddebc 100644
--- a/FortranRuntime/lib/Runtime/type-info.cpp
+++ b/flang-rt/lib/flang_rt/type-info.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/type-info.cpp -------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/type-info.cpp ------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/type-info.h b/flang-rt/lib/flang_rt/type-info.h
similarity index 98%
rename from FortranRuntime/lib/Runtime/type-info.h
rename to flang-rt/lib/flang_rt/type-info.h
index 150942547c2ee8..3b0b193d63379c 100644
--- a/FortranRuntime/lib/Runtime/type-info.h
+++ b/flang-rt/lib/flang_rt/type-info.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/type-info.h ---------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/type-info.h --------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,13 +6,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef FORTRAN_RUNTIME_TYPE_INFO_H_
-#define FORTRAN_RUNTIME_TYPE_INFO_H_
+#ifndef FORTRAN_FLANG_RT_TYPE_INFO_H_
+#define FORTRAN_FLANG_RT_TYPE_INFO_H_
 
 // A C++ perspective of the derived type description schemata in
 // flang/module/__fortran_type_info.f90.
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "terminator.h"
 #include "flang/Common/Fortran-consts.h"
 #include "flang/Common/bit-population-count.h"
@@ -321,4 +321,4 @@ class DerivedType {
 };
 
 } // namespace Fortran::runtime::typeInfo
-#endif /* FORTRAN_RUNTIME_TYPE_INFO_H_ */
+#endif /* FORTRAN_FLANG_RT_TYPE_INFO_H_ */
diff --git a/FortranRuntime/lib/Runtime/unit-map.cpp b/flang-rt/lib/flang_rt/unit-map.cpp
similarity index 98%
rename from FortranRuntime/lib/Runtime/unit-map.cpp
rename to flang-rt/lib/flang_rt/unit-map.cpp
index 93958be8df7ea5..0fda53ac071b27 100644
--- a/FortranRuntime/lib/Runtime/unit-map.cpp
+++ b/flang-rt/lib/flang_rt/unit-map.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit-map.cpp --------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit-map.cpp -------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/FortranRuntime/lib/Runtime/unit-map.h b/flang-rt/lib/flang_rt/unit-map.h
similarity index 93%
rename from FortranRuntime/lib/Runtime/unit-map.h
rename to flang-rt/lib/flang_rt/unit-map.h
index f37e2df7f3b15a..7215a5677f006b 100644
--- a/FortranRuntime/lib/Runtime/unit-map.h
+++ b/flang-rt/lib/flang_rt/unit-map.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit-map.h ----------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit-map.h ---------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,10 +9,10 @@
 // Maps Fortran unit numbers to their ExternalFileUnit instances.
 // A simple hash table with forward-linked chains per bucket.
 
-#ifndef FORTRAN_RUNTIME_UNIT_MAP_H_
-#define FORTRAN_RUNTIME_UNIT_MAP_H_
+#ifndef FORTRAN_FLANG_RT_UNIT_MAP_H_
+#define FORTRAN_FLANG_RT_UNIT_MAP_H_
 
-#include "FortranRuntime/Runtime/memory.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "lock.h"
 #include "unit.h"
 #include "flang/Common/fast-int-set.h"
@@ -100,4 +100,4 @@ class UnitMap {
   int emergencyNewUnit_{maxNewUnits_}; // not recycled
 };
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_UNIT_MAP_H_ */
+#endif /* FORTRAN_FLANG_RT_UNIT_MAP_H_ */
diff --git a/FortranRuntime/lib/Runtime/unit.cpp b/flang-rt/lib/flang_rt/unit.cpp
similarity index 99%
rename from FortranRuntime/lib/Runtime/unit.cpp
rename to flang-rt/lib/flang_rt/unit.cpp
index 496679ee8ce5f4..b5a4282faf22e5 100644
--- a/FortranRuntime/lib/Runtime/unit.cpp
+++ b/flang-rt/lib/flang_rt/unit.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit.cpp ------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit.cpp -----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -19,13 +19,13 @@
 
 namespace Fortran::runtime::io {
 
-#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#ifndef FLANGRT_NO_GLOBAL_VAR_DEFS
 RT_OFFLOAD_VAR_GROUP_BEGIN
 RT_VAR_ATTRS ExternalFileUnit *defaultInput{nullptr}; // unit 5
 RT_VAR_ATTRS ExternalFileUnit *defaultOutput{nullptr}; // unit 6
 RT_VAR_ATTRS ExternalFileUnit *errorOutput{nullptr}; // unit 0 extension
 RT_OFFLOAD_VAR_GROUP_END
-#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#endif // FLANGRT_NO_GLOBAL_VAR_DEFS
 
 RT_OFFLOAD_API_GROUP_BEGIN
 
diff --git a/FortranRuntime/lib/Runtime/unit.h b/flang-rt/lib/flang_rt/unit.h
similarity index 98%
rename from FortranRuntime/lib/Runtime/unit.h
rename to flang-rt/lib/flang_rt/unit.h
index 4a7444aedbe5b6..077a34833734ac 100644
--- a/FortranRuntime/lib/Runtime/unit.h
+++ b/flang-rt/lib/flang_rt/unit.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/unit.h --------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/unit.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,14 +8,14 @@
 
 // Fortran external I/O units
 
-#ifndef FORTRAN_RUNTIME_UNIT_H_
-#define FORTRAN_RUNTIME_UNIT_H_
+#ifndef FORTRAN_FLANG_RT_UNIT_H_
+#define FORTRAN_FLANG_RT_UNIT_H_
 
-#include "FortranRuntime/Runtime/memory.h"
 #include "buffer.h"
 #include "connection.h"
 #include "environment.h"
 #include "file.h"
+#include "flang-rt/flang_rt/memory.h"
 #include "format.h"
 #include "io-error.h"
 #include "io-stmt.h"
@@ -291,4 +291,4 @@ class ChildIo {
 };
 
 } // namespace Fortran::runtime::io
-#endif /* FORTRAN_RUNTIME_UNIT_H_ */
+#endif /* FORTRAN_FLANG_RT_UNIT_H_ */
diff --git a/FortranRuntime/lib/Runtime/utf.cpp b/flang-rt/lib/flang_rt/utf.cpp
similarity index 96%
rename from FortranRuntime/lib/Runtime/utf.cpp
rename to flang-rt/lib/flang_rt/utf.cpp
index 635451153d39a6..860db5f2367d38 100644
--- a/FortranRuntime/lib/Runtime/utf.cpp
+++ b/flang-rt/lib/flang_rt/utf.cpp
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/utf.cpp -------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/utf.cpp ------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,7 +10,7 @@
 
 namespace Fortran::runtime {
 
-#ifndef FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#ifndef FLANGRT_NO_GLOBAL_VAR_DEFS
 // clang-format off
 RT_OFFLOAD_VAR_GROUP_BEGIN
 const RT_CONST_VAR_ATTRS std::uint8_t UTF8FirstByteTable[256]{
@@ -41,7 +41,7 @@ const RT_CONST_VAR_ATTRS std::uint8_t UTF8FirstByteTable[256]{
 };
 RT_OFFLOAD_VAR_GROUP_END
 // clang-format on
-#endif // FLANG_RUNTIME_NO_GLOBAL_VAR_DEFS
+#endif // FLANGRT_NO_GLOBAL_VAR_DEFS
 
 RT_OFFLOAD_API_GROUP_BEGIN
 
diff --git a/FortranRuntime/lib/Runtime/utf.h b/flang-rt/lib/flang_rt/utf.h
similarity index 94%
rename from FortranRuntime/lib/Runtime/utf.h
rename to flang-rt/lib/flang_rt/utf.h
index 35c03fd4cdded5..71dc7b05a77513 100644
--- a/FortranRuntime/lib/Runtime/utf.h
+++ b/flang-rt/lib/flang_rt/utf.h
@@ -1,4 +1,4 @@
-//===-- lib/Runtime/utf.h ---------------------------------------*- C++ -*-===//
+//===-- lib/flang_rt/utf.h --------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -38,8 +38,8 @@
 // standard maximum.  However, we support extended forms up to 32 bits so that
 // CHARACTER(KIND=4) can be abused to hold arbitrary 32-bit data.
 
-#ifndef FORTRAN_RUNTIME_UTF_H_
-#define FORTRAN_RUNTIME_UTF_H_
+#ifndef FORTRAN_FLANG_RT_UTF_H_
+#define FORTRAN_FLANG_RT_UTF_H_
 
 #include "flang/Common/optional.h"
 #include <cstddef>
@@ -70,4 +70,4 @@ RT_API_ATTRS Fortran::common::optional<char32_t> DecodeUTF8(const char *);
 RT_API_ATTRS std::size_t EncodeUTF8(char *, char32_t);
 
 } // namespace Fortran::runtime
-#endif /* FORTRAN_RUNTIME_UTF_H_ */
+#endif /* FORTRAN_FLANG_RT_UTF_H_ */
diff --git a/FortranRuntime/test/CMakeLists.txt b/flang-rt/test/CMakeLists.txt
similarity index 57%
rename from FortranRuntime/test/CMakeLists.txt
rename to flang-rt/test/CMakeLists.txt
index c10c487d48c410..be42717b2834f3 100644
--- a/FortranRuntime/test/CMakeLists.txt
+++ b/flang-rt/test/CMakeLists.txt
@@ -25,7 +25,7 @@ configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.py
 )
 
-if (TARGET FortranRuntimeUnitTests)
+if (TARGET FlangRTUnitTests)
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/Unit/lit.site.cfg.py.in
     ${CMAKE_CURRENT_BINARY_DIR}/Unit/lit.site.cfg.py
@@ -41,29 +41,21 @@ if (TARGET FortranRuntimeUnitTests)
   )
 endif ()
 
-set(FORTRANRUNTIME_TEST_DEPENDS
-    FortranRuntimeUnitTests
-    FortranRuntime.static
+set(FLANGRT_TEST_DEPENDS
+    FlangRTUnitTests
+    flang_rt.unittest
   )
 
-add_custom_target(FortranRuntime-test-depends)
-set_target_properties(FortranRuntime-test-depends PROPERTIES FOLDER "Fortran Runtime/Meta")
-add_dependencies(FortranRuntime-test-depends ${FORTRANRUNTIME_TEST_DEPENDS})
+add_custom_target(flang-rt-test-depends)
+set_target_properties(flang-rt-test-depends PROPERTIES FOLDER "Fortran Runtime/Meta")
+add_dependencies(flang-rt-test-depends ${FLANGRT_TEST_DEPENDS})
 
-add_lit_testsuite(check-FortranRuntime "Running the FortranRuntime regression tests"
+add_lit_testsuite(check-flang-rt "Running the flang-rt regression tests"
   ${CMAKE_CURRENT_BINARY_DIR}
-  DEPENDS ${FORTRANRUNTIME_TEST_DEPENDS}
+  DEPENDS ${FLANGRT_TEST_DEPENDS}
 )
-set_target_properties(check-FortranRuntime PROPERTIES FOLDER "Fortran Runtime/Meta")
+set_target_properties(check-flang-rt PROPERTIES FOLDER "Fortran Runtime/Meta")
 
 
-add_lit_testsuites(FORTRANRUNTIME ${CMAKE_CURRENT_SOURCE_DIR}
-  DEPENDS ${FORTRANRUNTIME_TEST_DEPENDS})
-
-# To modify the default target triple for flang tests.
-if (DEFINED FLANG_TEST_TARGET_TRIPLE)
-  if (NOT DEFINED LLVM_TARGET_TRIPLE_ENV OR LLVM_TARGET_TRIPLE_ENV STREQUAL "")
-    message(FATAL_ERROR "LLVM_TARGET_TRIPLE_ENV must also be defined in order "
-                        "to use FLANG_TEST_TARGET_TRIPLE.")
-  endif()
-endif()
+add_lit_testsuites(flang-rt ${CMAKE_CURRENT_SOURCE_DIR}
+  DEPENDS ${FLANGRT_TEST_DEPENDS})
diff --git a/FortranRuntime/test/Driver/ctofortran.f90 b/flang-rt/test/Driver/ctofortran.f90
similarity index 100%
rename from FortranRuntime/test/Driver/ctofortran.f90
rename to flang-rt/test/Driver/ctofortran.f90
diff --git a/FortranRuntime/test/Driver/exec.f90 b/flang-rt/test/Driver/exec.f90
similarity index 100%
rename from FortranRuntime/test/Driver/exec.f90
rename to flang-rt/test/Driver/exec.f90
diff --git a/FortranRuntime/test/NonGtestUnit/lit.cfg.py b/flang-rt/test/NonGtestUnit/lit.cfg.py
similarity index 75%
rename from FortranRuntime/test/NonGtestUnit/lit.cfg.py
rename to flang-rt/test/NonGtestUnit/lit.cfg.py
index f807f2825a1bc7..20e28b0d3b55fd 100644
--- a/FortranRuntime/test/NonGtestUnit/lit.cfg.py
+++ b/flang-rt/test/NonGtestUnit/lit.cfg.py
@@ -5,18 +5,18 @@
 import lit.formats
 
 # name: The name of this test suite.
-config.name = "FortranRuntime-OldUnit"
+config.name = "flang-rt-OldUnit"
 
 # suffixes: A list of file extensions to treat as test files.
 # On Windows, ".exe" also matches the GTests and will execited redundantly.
 config.suffixes = [".test", ".exe"]
 
 # test_source_root: The root path where unit test binaries are located.
-config.test_source_root = os.path.join(config.fortranruntime_binary_dir, "unittests")
+config.test_source_root = os.path.join(config.flangrt_binary_dir, "unittests")
 
 # test_exec_root: The root path where tests should be run.
 # lit writes a '.lit_test_times.txt' file into this directory.
-config.test_exec_root = config.fortranruntime_binary_test_dir
+config.test_exec_root = config.flangrt_binary_test_dir
 
 # testFormat: The test format to use to interpret tests.
 config.test_format = lit.formats.ExecutableTest()
diff --git a/flang-rt/test/NonGtestUnit/lit.site.cfg.py.in b/flang-rt/test/NonGtestUnit/lit.site.cfg.py.in
new file mode 100644
index 00000000000000..9dc4d2d5a1513f
--- /dev/null
+++ b/flang-rt/test/NonGtestUnit/lit.site.cfg.py.in
@@ -0,0 +1,14 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+import os
+
+config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
+config.flangrt_source_dir = "@FLANGRT_SOURCE_DIR@"
+config.flangrt_binary_dir = "@FLANGRT_BINARY_DIR@"
+config.flangrt_binary_test_dir = os.path.dirname(__file__)
+
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
+# Let the main config do the real work.
+lit_config.load_config(config, os.path.join(config.flangrt_source_dir, 'test', 'NonGtestUnit', 'lit.cfg.py'))
diff --git a/FortranRuntime/test/Runtime/no-cpp-dep.c b/flang-rt/test/Runtime/no-cpp-dep.c
similarity index 87%
rename from FortranRuntime/test/Runtime/no-cpp-dep.c
rename to flang-rt/test/Runtime/no-cpp-dep.c
index 2cc5669a60d3a2..510816a07967ab 100644
--- a/FortranRuntime/test/Runtime/no-cpp-dep.c
+++ b/flang-rt/test/Runtime/no-cpp-dep.c
@@ -1,12 +1,12 @@
 /*
 This test makes sure that flang's runtime does not depend on the C++ runtime
-library. It tries to link this simple file against libFortranRuntime.a with
+library. It tries to link this simple file against libflang_rt.a with
 a C compiler.
 
 UNSUPPORTED: system-windows
 
-FIXME: This currently fails with CUDA-enabled FortranRuntime because it needs
-       to link libcuda_rt.
+FIXME: This currently fails with CUDA-enabled flang-rt because it needs
+       to link libcudart.
 
 RUN: %if system-aix %{ export OBJECT_MODE=64 %}
 RUN: %cc -std=c99 %s -I%include %libruntime -lm \
diff --git a/FortranRuntime/test/Unit/lit.cfg.py b/flang-rt/test/Unit/lit.cfg.py
similarity index 73%
rename from FortranRuntime/test/Unit/lit.cfg.py
rename to flang-rt/test/Unit/lit.cfg.py
index 888fb3981916c8..e46a78584c0425 100644
--- a/FortranRuntime/test/Unit/lit.cfg.py
+++ b/flang-rt/test/Unit/lit.cfg.py
@@ -5,17 +5,17 @@
 import lit.formats
 
 # name: The name of this test suite.
-config.name = "FortranRuntime-Unit"
+config.name = "flang-rt-Unit"
 
 # suffixes: A list of file extensions to treat as test files.
 config.suffixes = []
 
 # test_source_root: The root path where unit test binaries are located.
-config.test_source_root = os.path.join(config.fortranruntime_binary_dir, "unittests")
+config.test_source_root = os.path.join(config.flangrt_binary_dir, "unittests")
 
 # test_exec_root: The root path where tests should be run.
 # lit writes a '.lit_test_times.txt' file into this directory.
-config.test_exec_root = config.fortranruntime_binary_test_dir
+config.test_exec_root = config.flangrt_binary_test_dir
 
 # testFormat: The test format to use to interpret tests.
 config.test_format = lit.formats.GoogleTest(config.llvm_build_mode, "Tests")
diff --git a/flang-rt/test/Unit/lit.site.cfg.py.in b/flang-rt/test/Unit/lit.site.cfg.py.in
new file mode 100644
index 00000000000000..f6ed1e758d9374
--- /dev/null
+++ b/flang-rt/test/Unit/lit.site.cfg.py.in
@@ -0,0 +1,15 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+import os
+
+config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
+config.llvm_build_mode = "@LLVM_BUILD_MODE@"
+config.flangrt_source_dir = "@FLANGRT_SOURCE_DIR@"
+config.flangrt_binary_dir = "@FLANGRT_BINARY_DIR@"
+config.flangrt_binary_test_dir = os.path.dirname(__file__)
+
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
+# Let the main config do the real work.
+lit_config.load_config(config, os.path.join(config.flangrt_source_dir, 'test', 'Unit', 'lit.cfg.py'))
diff --git a/FortranRuntime/test/lit.cfg.py b/flang-rt/test/lit.cfg.py
similarity index 89%
rename from FortranRuntime/test/lit.cfg.py
rename to flang-rt/test/lit.cfg.py
index 1b9041111b72e8..1c3a08b3ae75b7 100644
--- a/FortranRuntime/test/lit.cfg.py
+++ b/flang-rt/test/lit.cfg.py
@@ -8,7 +8,7 @@
 # Configuration file for the 'lit' test runner.
 
 # name: The name of this test suite.
-config.name = "FortranRuntime"
+config.name = "flang-rt"
 
 # testFormat: The test format to use to interpret tests.
 #
@@ -54,7 +54,7 @@
 
 # test_exec_root: The root path where tests should be run.
 # lit writes a '.lit_test_times.txt' file into this directory.
-config.test_exec_root = config.fortranruntime_binary_test_dir
+config.test_exec_root = config.flangrt_binary_test_dir
 
 # On MacOS, -isysroot is needed to build binaries.
 isysroot_flag = []
@@ -72,7 +72,7 @@
 
 # Define some variables to help us test that the flang runtime doesn't depend on
 # the C++ runtime libraries. For this we need a C compiler.
-libruntime = os.path.join(config.fortranruntime_build_lib_dir, "libFortranRuntime.a")
+libruntime = os.path.join(config.flangrt_build_lib_dir, "libflang_rt.a")
 include = os.path.join(config.flang_source_dir, "include")
 tools.append(
     ToolSubst("%cc", command=config.cc, extra_args=isysroot_flag, unresolved="fatal")
@@ -80,7 +80,7 @@
 tools.append(ToolSubst("%libruntime", command=libruntime, unresolved="fatal"))
 tools.append(ToolSubst("%include", command=include, unresolved="fatal"))
 
-# Lwt tests find LLVM's standard tools (FileCheck, split-file, not, ...)
+# Let tests find LLVM's standard tools (FileCheck, split-file, not, ...)
 llvm_config.with_environment("PATH", config.llvm_tools_dir, append_path=True)
 
 llvm_config.add_tool_substitutions(tools)
diff --git a/flang-rt/test/lit.site.cfg.py.in b/flang-rt/test/lit.site.cfg.py.in
new file mode 100644
index 00000000000000..630f7dfcd508c7
--- /dev/null
+++ b/flang-rt/test/lit.site.cfg.py.in
@@ -0,0 +1,17 @@
+@LIT_SITE_CFG_IN_HEADER@
+
+import sys
+
+config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
+config.flang_source_dir = "@FLANG_SOURCE_DIR@"
+config.flangrt_source_dir = "@FLANGRT_SOURCE_DIR@"
+config.flangrt_binary_test_dir = os.path.dirname(__file__)
+config.flangrt_build_lib_dir = "@FLANGRT_BUILD_LIB_DIR@"
+config.cc = "@CMAKE_C_COMPILER@"
+config.osx_sysroot = path(r"@CMAKE_OSX_SYSROOT@")
+
+import lit.llvm
+lit.llvm.initialize(lit_config, config)
+
+# Let the main config do the real work.
+lit_config.load_config(config, os.path.join(config.flangrt_source_dir, 'test', 'lit.cfg.py'))
diff --git a/FortranRuntime/unittests/CMakeLists.txt b/flang-rt/unittests/CMakeLists.txt
similarity index 72%
rename from FortranRuntime/unittests/CMakeLists.txt
rename to flang-rt/unittests/CMakeLists.txt
index 592f2ef7ce42ab..d6ed84c9f72bf0 100644
--- a/FortranRuntime/unittests/CMakeLists.txt
+++ b/flang-rt/unittests/CMakeLists.txt
@@ -26,13 +26,13 @@ endif()
 
 
 # Target that depends on all unittests
-add_custom_target(FortranRuntimeUnitTests)
-set_target_properties(FortranRuntimeUnitTests PROPERTIES FOLDER "Fortran Runtime/Meta")
+add_custom_target(FlangRTUnitTests)
+set_target_properties(FlangRTUnitTests PROPERTIES FOLDER "Fortran Runtime/Meta")
 
 
-function(add_fortranruntime_unittest_offload_properties target)
+function(add_flangrt_unittest_offload_properties target)
   # Set CUDA_RESOLVE_DEVICE_SYMBOLS.
-  if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
+  if (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "CUDA")
     set_target_properties(${target}
       PROPERTIES CUDA_RESOLVE_DEVICE_SYMBOLS ON
       )
@@ -43,7 +43,7 @@ function(add_fortranruntime_unittest_offload_properties target)
   #
   # FIXME: replace 'native' in --offload-arch option with the list
   #        of targets that Fortran Runtime was built for.
-  if (FORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
+  if (FLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT STREQUAL "OpenMP")
     set_target_properties(${target}
       PROPERTIES LINK_OPTIONS
       "-fopenmp;--offload-arch=native"
@@ -52,22 +52,22 @@ function(add_fortranruntime_unittest_offload_properties target)
 endfunction()
 
 
-function(add_fortranruntime_unittest test_dirname)
+function(add_flangrt_unittest test_dirname)
   cmake_parse_arguments(ARG
     ""
     ""
     "LINK_LIBS"
     ${ARGN})
 
-  add_unittest(FortranRuntimeUnitTests ${test_dirname} ${ARG_UNPARSED_ARGUMENTS})
+  add_unittest(FlangRTUnitTests ${test_dirname} ${ARG_UNPARSED_ARGUMENTS})
 
-  target_include_directories(${test_dirname} PRIVATE "${FORTRANRUNTIME_SOURCE_DIR}/include")
+  target_include_directories(${test_dirname} PRIVATE "${FLANGRT_SOURCE_DIR}/include")
   target_include_directories(${test_dirname} PRIVATE "${FLANG_SOURCE_DIR}/include")
   target_link_libraries(${test_dirname} PRIVATE ${ARG_LINK_LIBS})
-  add_fortranruntime_unittest_offload_properties(${test_dirname})
+  add_flangrt_unittest_offload_properties(${test_dirname})
 endfunction()
 
-function(add_fortranruntime_nongtest_unittest test_name)
+function(add_flangrt_nongtest_unittest test_name)
   cmake_parse_arguments(ARG
     "SLOW_TEST"
     ""
@@ -83,15 +83,15 @@ function(add_fortranruntime_nongtest_unittest test_name)
   add_executable(${test_name}${suffix} ${ARG_UNPARSED_ARGUMENTS})
   set_target_properties(${test_name}${suffix} PROPERTIES FOLDER "Fortran Runtime/Tests/Unit")
 
-  target_include_directories(${test_name}${suffix} PRIVATE "${FORTRANRUNTIME_SOURCE_DIR}/include")
+  target_include_directories(${test_name}${suffix} PRIVATE "${FLANGRT_SOURCE_DIR}/include")
   target_include_directories(${test_name}${suffix} PRIVATE "${FLANG_SOURCE_DIR}/include")
   target_link_libraries(${test_name}${suffix} PRIVATE NonGTestTesting ${ARG_LINK_LIBS})
 
   if(NOT ARG_SLOW_TEST)
-    add_dependencies(FortranRuntimeUnitTests ${test_name}${suffix})
+    add_dependencies(FlangRTUnitTests ${test_name}${suffix})
   endif()
 
-  add_fortranruntime_unittest_offload_properties(${test_name}${suffix})
+  add_flangrt_unittest_offload_properties(${test_name}${suffix})
 endfunction()
 
 add_subdirectory(Evaluate)
diff --git a/FortranRuntime/unittests/Evaluate/CMakeLists.txt b/flang-rt/unittests/Evaluate/CMakeLists.txt
similarity index 73%
rename from FortranRuntime/unittests/Evaluate/CMakeLists.txt
rename to flang-rt/unittests/Evaluate/CMakeLists.txt
index fd3a5755dd1227..dd4b729f698cf6 100644
--- a/FortranRuntime/unittests/Evaluate/CMakeLists.txt
+++ b/flang-rt/unittests/Evaluate/CMakeLists.txt
@@ -6,14 +6,14 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_nongtest_unittest(reshape
+add_flangrt_nongtest_unittest(reshape
   reshape.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
 
-add_fortranruntime_nongtest_unittest(ISO-Fortran-binding
+add_flangrt_nongtest_unittest(ISO-Fortran-binding
   ISO-Fortran-binding.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
diff --git a/FortranRuntime/unittests/Evaluate/ISO-Fortran-binding.cpp b/flang-rt/unittests/Evaluate/ISO-Fortran-binding.cpp
similarity index 99%
rename from FortranRuntime/unittests/Evaluate/ISO-Fortran-binding.cpp
rename to flang-rt/unittests/Evaluate/ISO-Fortran-binding.cpp
index b68dfbcbd5b335..03cc59291787aa 100644
--- a/FortranRuntime/unittests/Evaluate/ISO-Fortran-binding.cpp
+++ b/flang-rt/unittests/Evaluate/ISO-Fortran-binding.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
 #include "flang/Testing/testing.h"
 #include "llvm/Support/raw_ostream.h"
diff --git a/FortranRuntime/unittests/Evaluate/reshape.cpp b/flang-rt/unittests/Evaluate/reshape.cpp
similarity index 98%
rename from FortranRuntime/unittests/Evaluate/reshape.cpp
rename to flang-rt/unittests/Evaluate/reshape.cpp
index 0233ab37e25c6e..c9ead4fe744f91 100644
--- a/FortranRuntime/unittests/Evaluate/reshape.cpp
+++ b/flang-rt/unittests/Evaluate/reshape.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "flang/Runtime/transformational.h"
 #include "flang/Testing/testing.h"
 #include <cinttypes>
diff --git a/FortranRuntime/unittests/Runtime/AccessTest.cpp b/flang-rt/unittests/Runtime/AccessTest.cpp
similarity index 100%
rename from FortranRuntime/unittests/Runtime/AccessTest.cpp
rename to flang-rt/unittests/Runtime/AccessTest.cpp
diff --git a/FortranRuntime/unittests/Runtime/Allocatable.cpp b/flang-rt/unittests/Runtime/Allocatable.cpp
similarity index 100%
rename from FortranRuntime/unittests/Runtime/Allocatable.cpp
rename to flang-rt/unittests/Runtime/Allocatable.cpp
diff --git a/FortranRuntime/unittests/Runtime/ArrayConstructor.cpp b/flang-rt/unittests/Runtime/ArrayConstructor.cpp
similarity index 97%
rename from FortranRuntime/unittests/Runtime/ArrayConstructor.cpp
rename to flang-rt/unittests/Runtime/ArrayConstructor.cpp
index 9d9a4ddae8689f..c52ce8e4ea54fd 100644
--- a/FortranRuntime/unittests/Runtime/ArrayConstructor.cpp
+++ b/flang-rt/unittests/Runtime/ArrayConstructor.cpp
@@ -6,9 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/array-constructor.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/array-constructor.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"
diff --git a/FortranRuntime/unittests/Runtime/BufferTest.cpp b/flang-rt/unittests/Runtime/BufferTest.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/BufferTest.cpp
rename to flang-rt/unittests/Runtime/BufferTest.cpp
index 9a7dd86d0c1dc6..41c660e638e712 100644
--- a/FortranRuntime/unittests/Runtime/BufferTest.cpp
+++ b/flang-rt/unittests/Runtime/BufferTest.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "../../lib/Runtime/buffer.h"
+#include "../../lib/flang_rt/buffer.h"
 #include "CrashHandlerFixture.h"
 #include "gtest/gtest.h"
 #include <algorithm>
diff --git a/FortranRuntime/unittests/Runtime/CMakeLists.txt b/flang-rt/unittests/Runtime/CMakeLists.txt
similarity index 90%
rename from FortranRuntime/unittests/Runtime/CMakeLists.txt
rename to flang-rt/unittests/Runtime/CMakeLists.txt
index e4439dcc8b3c7e..ce15fe5ef74f96 100644
--- a/FortranRuntime/unittests/Runtime/CMakeLists.txt
+++ b/flang-rt/unittests/Runtime/CMakeLists.txt
@@ -6,7 +6,7 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_unittest(FlangRuntimeTests
+add_flangrt_unittest(RuntimeTests
   AccessTest.cpp
   Allocatable.cpp
   ArrayConstructor.cpp
@@ -38,9 +38,9 @@ add_fortranruntime_unittest(FlangRuntimeTests
   TemporaryStack.cpp
   Transformational.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
 
-if (FORTRANRUNTIME_ENABLE_CUF)
+if (FLANG_RT_ENABLE_CUF)
   add_subdirectory(CUDA)
 endif ()
diff --git a/FortranRuntime/unittests/Runtime/CUDA/AllocatorCUF.cpp b/flang-rt/unittests/Runtime/CUDA/AllocatorCUF.cpp
similarity index 90%
rename from FortranRuntime/unittests/Runtime/CUDA/AllocatorCUF.cpp
rename to flang-rt/unittests/Runtime/CUDA/AllocatorCUF.cpp
index d2a2e5a11abf80..46461a863c0696 100644
--- a/FortranRuntime/unittests/Runtime/CUDA/AllocatorCUF.cpp
+++ b/flang-rt/unittests/Runtime/CUDA/AllocatorCUF.cpp
@@ -6,16 +6,16 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/CUDA/allocator.h"
-#include "FortranRuntime/Runtime/CUDA/descriptor.h"
-#include "FortranRuntime/Runtime/allocatable.h"
-#include "FortranRuntime/Runtime/allocator-registry.h"
+#include "cuda_runtime.h"
+#include "flang-rt/flang_rt/allocator-registry.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
-#include "../../../runtime/terminator.h"
+#include "../../../lib/flang_rt/terminator.h"
+#include "flang-rt/CufRuntime/allocator.h"
+#include "flang/Runtime/CUDA/descriptor.h"
+#include "flang/Runtime/allocatable.h"
 #include "flang/Support/Fortran.h"
 
-#include "cuda_runtime.h"
-
 using namespace Fortran::runtime;
 using namespace Fortran::runtime::cuda;
 
diff --git a/FortranRuntime/unittests/Runtime/CUDA/CMakeLists.txt b/flang-rt/unittests/Runtime/CUDA/CMakeLists.txt
similarity index 89%
rename from FortranRuntime/unittests/Runtime/CUDA/CMakeLists.txt
rename to flang-rt/unittests/Runtime/CUDA/CMakeLists.txt
index 04321e65d733ad..829ae9250f345e 100644
--- a/FortranRuntime/unittests/Runtime/CUDA/CMakeLists.txt
+++ b/flang-rt/unittests/Runtime/CUDA/CMakeLists.txt
@@ -6,14 +6,14 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_unittest(FlangCufRuntimeTests
+add_flangrt_unittest(FlangCufRuntimeTests
   AllocatorCUF.cpp
 )
 
 target_link_libraries(FlangCufRuntimeTests
   PRIVATE
   CufRuntime_cuda_${CUDAToolkit_VERSION_MAJOR}
-  FortranRuntime
+  flang_rt
 )
 
 target_include_directories(FlangCufRuntimeTests PRIVATE ${CUDAToolkit_INCLUDE_DIRS})
diff --git a/FortranRuntime/unittests/Runtime/CharacterTest.cpp b/flang-rt/unittests/Runtime/CharacterTest.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/CharacterTest.cpp
rename to flang-rt/unittests/Runtime/CharacterTest.cpp
index 610061e2122cd5..3a4b5706e53849 100644
--- a/FortranRuntime/unittests/Runtime/CharacterTest.cpp
+++ b/flang-rt/unittests/Runtime/CharacterTest.cpp
@@ -10,7 +10,7 @@
 // in Fortran.
 
 #include "flang/Runtime/character.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include <cstring>
 #include <functional>
diff --git a/FortranRuntime/unittests/Runtime/CommandTest.cpp b/flang-rt/unittests/Runtime/CommandTest.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/CommandTest.cpp
rename to flang-rt/unittests/Runtime/CommandTest.cpp
index a7d68508c5abca..15b2ed2e42bba1 100644
--- a/FortranRuntime/unittests/Runtime/CommandTest.cpp
+++ b/flang-rt/unittests/Runtime/CommandTest.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/command.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/execute.h"
diff --git a/FortranRuntime/unittests/Runtime/Complex.cpp b/flang-rt/unittests/Runtime/Complex.cpp
similarity index 100%
rename from FortranRuntime/unittests/Runtime/Complex.cpp
rename to flang-rt/unittests/Runtime/Complex.cpp
diff --git a/FortranRuntime/unittests/Runtime/CrashHandlerFixture.cpp b/flang-rt/unittests/Runtime/CrashHandlerFixture.cpp
similarity index 96%
rename from FortranRuntime/unittests/Runtime/CrashHandlerFixture.cpp
rename to flang-rt/unittests/Runtime/CrashHandlerFixture.cpp
index 5e0b746c7e974a..3959b0d4b78809 100644
--- a/FortranRuntime/unittests/Runtime/CrashHandlerFixture.cpp
+++ b/flang-rt/unittests/Runtime/CrashHandlerFixture.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 #include "CrashHandlerFixture.h"
-#include "../../lib/Runtime/terminator.h"
+#include "../../lib/flang_rt/terminator.h"
 #include <cstdarg>
 #include <cstdlib>
 
diff --git a/FortranRuntime/unittests/Runtime/CrashHandlerFixture.h b/flang-rt/unittests/Runtime/CrashHandlerFixture.h
similarity index 100%
rename from FortranRuntime/unittests/Runtime/CrashHandlerFixture.h
rename to flang-rt/unittests/Runtime/CrashHandlerFixture.h
diff --git a/FortranRuntime/unittests/Runtime/Derived.cpp b/flang-rt/unittests/Runtime/Derived.cpp
similarity index 98%
rename from FortranRuntime/unittests/Runtime/Derived.cpp
rename to flang-rt/unittests/Runtime/Derived.cpp
index 22361352fdf5d9..055174a3b5a907 100644
--- a/FortranRuntime/unittests/Runtime/Derived.cpp
+++ b/flang-rt/unittests/Runtime/Derived.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/derived-api.h"
diff --git a/FortranRuntime/unittests/Runtime/ExternalIOTest.cpp b/flang-rt/unittests/Runtime/ExternalIOTest.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/ExternalIOTest.cpp
rename to flang-rt/unittests/Runtime/ExternalIOTest.cpp
index 7ff4aa3c14bdc5..a93ee97da8f5f7 100644
--- a/FortranRuntime/unittests/Runtime/ExternalIOTest.cpp
+++ b/flang-rt/unittests/Runtime/ExternalIOTest.cpp
@@ -11,8 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/main.h"
 #include "flang/Runtime/stop.h"
diff --git a/FortranRuntime/unittests/Runtime/Format.cpp b/flang-rt/unittests/Runtime/Format.cpp
similarity index 97%
rename from FortranRuntime/unittests/Runtime/Format.cpp
rename to flang-rt/unittests/Runtime/Format.cpp
index f1447608917f2d..3012806a8eacc1 100644
--- a/FortranRuntime/unittests/Runtime/Format.cpp
+++ b/flang-rt/unittests/Runtime/Format.cpp
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "../../lib/Runtime/connection.h"
-#include "../../lib/Runtime/format-implementation.h"
-#include "../../lib/Runtime/io-error.h"
+#include "../../lib/flang_rt/connection.h"
+#include "../../lib/flang_rt/format-implementation.h"
+#include "../../lib/flang_rt/io-error.h"
 #include <optional>
 #include <string>
 #include <tuple>
diff --git a/FortranRuntime/unittests/Runtime/Inquiry.cpp b/flang-rt/unittests/Runtime/Inquiry.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/Inquiry.cpp
rename to flang-rt/unittests/Runtime/Inquiry.cpp
index 3e5f0037177f1c..0bda07aaef295c 100644
--- a/FortranRuntime/unittests/Runtime/Inquiry.cpp
+++ b/flang-rt/unittests/Runtime/Inquiry.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/inquiry.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 
diff --git a/FortranRuntime/unittests/Runtime/ListInputTest.cpp b/flang-rt/unittests/Runtime/ListInputTest.cpp
similarity index 98%
rename from FortranRuntime/unittests/Runtime/ListInputTest.cpp
rename to flang-rt/unittests/Runtime/ListInputTest.cpp
index e0fe4dfeac3949..7e04ab834eb247 100644
--- a/FortranRuntime/unittests/Runtime/ListInputTest.cpp
+++ b/flang-rt/unittests/Runtime/ListInputTest.cpp
@@ -7,9 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
-#include "../../lib/Runtime/io-error.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
+#include "../../lib/flang_rt/io-error.h"
 
 using namespace Fortran::runtime;
 using namespace Fortran::runtime::io;
diff --git a/FortranRuntime/unittests/Runtime/LogicalFormatTest.cpp b/flang-rt/unittests/Runtime/LogicalFormatTest.cpp
similarity index 95%
rename from FortranRuntime/unittests/Runtime/LogicalFormatTest.cpp
rename to flang-rt/unittests/Runtime/LogicalFormatTest.cpp
index 9fa0c2f4260edb..b5a9e2d317841f 100644
--- a/FortranRuntime/unittests/Runtime/LogicalFormatTest.cpp
+++ b/flang-rt/unittests/Runtime/LogicalFormatTest.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include <algorithm>
 #include <array>
 #include <cstring>
diff --git a/FortranRuntime/unittests/Runtime/Matmul.cpp b/flang-rt/unittests/Runtime/Matmul.cpp
similarity index 98%
rename from FortranRuntime/unittests/Runtime/Matmul.cpp
rename to flang-rt/unittests/Runtime/Matmul.cpp
index 6eb4012e785ff1..e833b3861badac 100644
--- a/FortranRuntime/unittests/Runtime/Matmul.cpp
+++ b/flang-rt/unittests/Runtime/Matmul.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/matmul.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"
diff --git a/FortranRuntime/unittests/Runtime/MatmulTranspose.cpp b/flang-rt/unittests/Runtime/MatmulTranspose.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/MatmulTranspose.cpp
rename to flang-rt/unittests/Runtime/MatmulTranspose.cpp
index 199062f820c303..560f62935e35bc 100644
--- a/FortranRuntime/unittests/Runtime/MatmulTranspose.cpp
+++ b/flang-rt/unittests/Runtime/MatmulTranspose.cpp
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"
diff --git a/FortranRuntime/unittests/Runtime/MiscIntrinsic.cpp b/flang-rt/unittests/Runtime/MiscIntrinsic.cpp
similarity index 98%
rename from FortranRuntime/unittests/Runtime/MiscIntrinsic.cpp
rename to flang-rt/unittests/Runtime/MiscIntrinsic.cpp
index 1033dda9d636f7..ca3a3e4fd3b839 100644
--- a/FortranRuntime/unittests/Runtime/MiscIntrinsic.cpp
+++ b/flang-rt/unittests/Runtime/MiscIntrinsic.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Runtime/allocatable.h"
diff --git a/FortranRuntime/unittests/Runtime/Namelist.cpp b/flang-rt/unittests/Runtime/Namelist.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/Namelist.cpp
rename to flang-rt/unittests/Runtime/Namelist.cpp
index 544ab85234fd65..d30625f23bfc1c 100644
--- a/FortranRuntime/unittests/Runtime/Namelist.cpp
+++ b/flang-rt/unittests/Runtime/Namelist.cpp
@@ -6,10 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "../../lib/Runtime/namelist.h"
+#include "../../lib/flang_rt/namelist.h"
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include "tools.h"
 #include <algorithm>
 #include <cinttypes>
diff --git a/FortranRuntime/unittests/Runtime/Numeric.cpp b/flang-rt/unittests/Runtime/Numeric.cpp
similarity index 100%
rename from FortranRuntime/unittests/Runtime/Numeric.cpp
rename to flang-rt/unittests/Runtime/Numeric.cpp
diff --git a/FortranRuntime/unittests/Runtime/NumericalFormatTest.cpp b/flang-rt/unittests/Runtime/NumericalFormatTest.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/NumericalFormatTest.cpp
rename to flang-rt/unittests/Runtime/NumericalFormatTest.cpp
index c588c739686bed..6c11bb0d4a49d6 100644
--- a/FortranRuntime/unittests/Runtime/NumericalFormatTest.cpp
+++ b/flang-rt/unittests/Runtime/NumericalFormatTest.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "CrashHandlerFixture.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/io-api-funcs.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/io-api-funcs.h"
 #include <algorithm>
 #include <array>
 #include <cstring>
diff --git a/FortranRuntime/unittests/Runtime/Pointer.cpp b/flang-rt/unittests/Runtime/Pointer.cpp
similarity index 98%
rename from FortranRuntime/unittests/Runtime/Pointer.cpp
rename to flang-rt/unittests/Runtime/Pointer.cpp
index 733cd42232875f..c787ed9e71eee9 100644
--- a/FortranRuntime/unittests/Runtime/Pointer.cpp
+++ b/flang-rt/unittests/Runtime/Pointer.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/pointer.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 
diff --git a/FortranRuntime/unittests/Runtime/Ragged.cpp b/flang-rt/unittests/Runtime/Ragged.cpp
similarity index 100%
rename from FortranRuntime/unittests/Runtime/Ragged.cpp
rename to flang-rt/unittests/Runtime/Ragged.cpp
diff --git a/FortranRuntime/unittests/Runtime/Random.cpp b/flang-rt/unittests/Runtime/Random.cpp
similarity index 95%
rename from FortranRuntime/unittests/Runtime/Random.cpp
rename to flang-rt/unittests/Runtime/Random.cpp
index 81497a682660a8..bd4fcfd5e87975 100644
--- a/FortranRuntime/unittests/Runtime/Random.cpp
+++ b/flang-rt/unittests/Runtime/Random.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/random.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include <cmath>
 
diff --git a/FortranRuntime/unittests/Runtime/Reduction.cpp b/flang-rt/unittests/Runtime/Reduction.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/Reduction.cpp
rename to flang-rt/unittests/Runtime/Reduction.cpp
index a382f4b7a71770..0f3789b017c6f6 100644
--- a/FortranRuntime/unittests/Runtime/Reduction.cpp
+++ b/flang-rt/unittests/Runtime/Reduction.cpp
@@ -7,8 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/reduction.h"
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Common/float128.h"
diff --git a/FortranRuntime/unittests/Runtime/RuntimeCrashTest.cpp b/flang-rt/unittests/Runtime/RuntimeCrashTest.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/RuntimeCrashTest.cpp
rename to flang-rt/unittests/Runtime/RuntimeCrashTest.cpp
index 7ce1ee796d739b..f1ea6c897d515e 100644
--- a/FortranRuntime/unittests/Runtime/RuntimeCrashTest.cpp
+++ b/flang-rt/unittests/Runtime/RuntimeCrashTest.cpp
@@ -12,7 +12,7 @@
 //===----------------------------------------------------------------------===//
 #include "CrashHandlerFixture.h"
 #include "tools.h"
-#include "../../lib/Runtime/terminator.h"
+#include "../../lib/flang_rt/terminator.h"
 #include "flang/Runtime/io-api.h"
 #include "flang/Runtime/transformational.h"
 #include <gtest/gtest.h>
diff --git a/FortranRuntime/unittests/Runtime/Stop.cpp b/flang-rt/unittests/Runtime/Stop.cpp
similarity index 98%
rename from FortranRuntime/unittests/Runtime/Stop.cpp
rename to flang-rt/unittests/Runtime/Stop.cpp
index c12ec097068438..9aaabc2e6c6384 100644
--- a/FortranRuntime/unittests/Runtime/Stop.cpp
+++ b/flang-rt/unittests/Runtime/Stop.cpp
@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 #include "flang/Runtime/stop.h"
 #include "CrashHandlerFixture.h"
-#include "../../lib/Runtime/environment.h"
+#include "../../lib/flang_rt/environment.h"
 #include <cstdlib>
 #include <gtest/gtest.h>
 
diff --git a/FortranRuntime/unittests/Runtime/Support.cpp b/flang-rt/unittests/Runtime/Support.cpp
similarity index 98%
rename from FortranRuntime/unittests/Runtime/Support.cpp
rename to flang-rt/unittests/Runtime/Support.cpp
index 05328e6baa411c..d37369df025f45 100644
--- a/FortranRuntime/unittests/Runtime/Support.cpp
+++ b/flang-rt/unittests/Runtime/Support.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/support.h"
-#include "FortranRuntime/Runtime/descriptor.h"
+#include "flang-rt/flang_rt/descriptor.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 
diff --git a/FortranRuntime/unittests/Runtime/TemporaryStack.cpp b/flang-rt/unittests/Runtime/TemporaryStack.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/TemporaryStack.cpp
rename to flang-rt/unittests/Runtime/TemporaryStack.cpp
index b0b1041f0f09e7..8a9f2dfe6d22f1 100644
--- a/FortranRuntime/unittests/Runtime/TemporaryStack.cpp
+++ b/flang-rt/unittests/Runtime/TemporaryStack.cpp
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Common/ISO_Fortran_binding_wrapper.h"
diff --git a/FortranRuntime/unittests/Runtime/Time.cpp b/flang-rt/unittests/Runtime/Time.cpp
similarity index 100%
rename from FortranRuntime/unittests/Runtime/Time.cpp
rename to flang-rt/unittests/Runtime/Time.cpp
diff --git a/FortranRuntime/unittests/Runtime/Transformational.cpp b/flang-rt/unittests/Runtime/Transformational.cpp
similarity index 99%
rename from FortranRuntime/unittests/Runtime/Transformational.cpp
rename to flang-rt/unittests/Runtime/Transformational.cpp
index 6b8903750d0aec..e8981e9b122eb7 100644
--- a/FortranRuntime/unittests/Runtime/Transformational.cpp
+++ b/flang-rt/unittests/Runtime/Transformational.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/transformational.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "tools.h"
 #include "flang/Common/float128.h"
diff --git a/FortranRuntime/unittests/Runtime/tools.h b/flang-rt/unittests/Runtime/tools.h
similarity index 95%
rename from FortranRuntime/unittests/Runtime/tools.h
rename to flang-rt/unittests/Runtime/tools.h
index 8000d83fc0c394..7edeff7f7eb579 100644
--- a/FortranRuntime/unittests/Runtime/tools.h
+++ b/flang-rt/unittests/Runtime/tools.h
@@ -9,8 +9,8 @@
 #ifndef FORTRAN_UNITTESTS_RUNTIME_TOOLS_H_
 #define FORTRAN_UNITTESTS_RUNTIME_TOOLS_H_
 
-#include "FortranRuntime/Runtime/descriptor.h"
-#include "FortranRuntime/Runtime/type-code.h"
+#include "flang-rt/flang_rt/descriptor.h"
+#include "flang-rt/flang_rt/type-code.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/allocatable.h"
 #include "flang/Runtime/cpp-type.h"
diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
index ac189de2386b16..34c5661c963a80 100644
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@@ -23,7 +23,6 @@ if (LLVM_ENABLE_EH)
 endif()
 
 set(FLANG_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
-set(FORTRANRUNTIME_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../FortranRuntime")
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE)
   message(FATAL_ERROR "In-source builds are not allowed. \
@@ -247,13 +246,11 @@ set(LLVM_BUILD_TOOLS ON)
 
 include_directories(BEFORE
   ${FLANG_BINARY_DIR}/include
-  ${FLANG_SOURCE_DIR}/include
-  ${FORTRANRUNTIME_SOURCE_DIR}/include)
+  ${FLANG_SOURCE_DIR}/include)
 
 # Add Flang-centric modules to cmake path.
 list(INSERT CMAKE_MODULE_PATH 0
   "${FLANG_SOURCE_DIR}/cmake/modules"
-  "${FORTRANRUNTIME_SOURCE_DIR}/cmake/modules"
   "${LLVM_COMMON_CMAKE_UTILS}/Modules"
   )
 include(AddFlang)
@@ -271,7 +268,7 @@ set(FLANG_DEFAULT_LINKER "" CACHE STRING
   "Default linker to use (linker name or absolute path, empty for platform default)")
 
 set(FLANG_DEFAULT_RTLIB "" CACHE STRING
-   "Default Fortran runtime library to use (\"libFortranRuntime\"), leave empty for platform default.")
+   "Default Fortran runtime library to use (\"libflang_rt\"), leave empty for platform default.")
 
 if (NOT(FLANG_DEFAULT_RTLIB STREQUAL ""))
   message(WARNING "Resetting Flang's default runtime library to use platform default.")
diff --git a/FortranRuntime/cmake/modules/FlangCommon.cmake b/flang/cmake/modules/FlangCommon.cmake
similarity index 93%
rename from FortranRuntime/cmake/modules/FlangCommon.cmake
rename to flang/cmake/modules/FlangCommon.cmake
index d7194ad4d7ef56..1b8606843b2240 100644
--- a/FortranRuntime/cmake/modules/FlangCommon.cmake
+++ b/flang/cmake/modules/FlangCommon.cmake
@@ -1,43 +1,43 @@
-#===-- cmake/modules/FlangCommon.txt ----------------------------===#
-#
-# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-# See https://llvm.org/LICENSE.txt for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#
-#===------------------------------------------------------------------------===#
-#
-# CMake definitions shared betwween Flang and FortranRuntime
-#
-#===------------------------------------------------------------------------===#
-
-# The out of tree builds of the compiler and the Fortran runtime
-# must use the same setting of FLANG_RUNTIME_F128_MATH_LIB
-# to be composable. Failure to synchronize this setting may result
-# in linking errors or fatal failures in F128 runtime functions.
-set(FLANG_RUNTIME_F128_MATH_LIB "" CACHE STRING
-  "Specifies the target library used for implementing IEEE-754 128-bit float \
-  math in F18 runtime, e.g. it might be libquadmath for targets where \
-  REAL(16) is mapped to __float128, or libm for targets where REAL(16) \
-  is mapped to long double, etc."
-  )
-if (FLANG_RUNTIME_F128_MATH_LIB)
-  add_compile_definitions(FLANG_RUNTIME_F128_MATH_LIB="${FLANG_RUNTIME_F128_MATH_LIB}")
-endif()
-
-# Check if 128-bit float computations can be done via long double
-check_cxx_source_compiles(
-  "#include <cfloat>
-   #if LDBL_MANT_DIG != 113
-   #error LDBL_MANT_DIG != 113
-   #endif
-   int main() { return 0; }
-  "
-  HAVE_LDBL_MANT_DIG_113)
-
-include(TestBigEndian)
-test_big_endian(IS_BIGENDIAN)
-if (IS_BIGENDIAN)
-  add_compile_definitions(FLANG_BIG_ENDIAN=1)
-else ()
-  add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
-endif ()
+#===-- cmake/modules/FlangCommon.txt ----------------------------===#
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+#===------------------------------------------------------------------------===#
+#
+# CMake definitions shared between Flang and Flang-RT
+#
+#===------------------------------------------------------------------------===#
+
+# The out of tree builds of the compiler and the Fortran runtime
+# must use the same setting of FLANG_RUNTIME_F128_MATH_LIB
+# to be composable. Failure to synchronize this setting may result
+# in linking errors or fatal failures in F128 runtime functions.
+set(FLANG_RUNTIME_F128_MATH_LIB "" CACHE STRING
+  "Specifies the target library used for implementing IEEE-754 128-bit float \
+  math in F18 runtime, e.g. it might be libquadmath for targets where \
+  REAL(16) is mapped to __float128, or libm for targets where REAL(16) \
+  is mapped to long double, etc."
+  )
+if (FLANG_RUNTIME_F128_MATH_LIB)
+  add_compile_definitions(FLANG_RUNTIME_F128_MATH_LIB="${FLANG_RUNTIME_F128_MATH_LIB}")
+endif()
+
+# Check if 128-bit float computations can be done via long double
+check_cxx_source_compiles(
+  "#include <cfloat>
+   #if LDBL_MANT_DIG != 113
+   #error LDBL_MANT_DIG != 113
+   #endif
+   int main() { return 0; }
+  "
+  HAVE_LDBL_MANT_DIG_113)
+
+include(TestBigEndian)
+test_big_endian(IS_BIGENDIAN)
+if (IS_BIGENDIAN)
+  add_compile_definitions(FLANG_BIG_ENDIAN=1)
+else ()
+  add_compile_definitions(FLANG_LITTLE_ENDIAN=1)
+endif ()
diff --git a/flang/docs/FlangDriver.md b/flang/docs/FlangDriver.md
index 98611ee338e706..5165ac6c323ac2 100644
--- a/flang/docs/FlangDriver.md
+++ b/flang/docs/FlangDriver.md
@@ -179,18 +179,18 @@ like this:
 
 ```
 $ flang -v -o example example.o
-"/usr/bin/ld" [...] example.o [...] "-lFortranRuntime" [...]
+"/usr/bin/ld" [...] example.o [...] "-lflang_rt" [...]
 ```
 
 The automatically added libraries are:
 
-* `FortranRuntime`: Provides most of the Flang runtime library.
+* `flang_rt`: Provides most of the Flang runtime library.
 
 If the code is C/C++ based and invokes Fortran routines, one can either use Clang
 or Flang as the linker driver.  If Clang is used, it will automatically all
 required runtime libraries needed by C++ (e.g., for STL) to the linker invocation.
-In this case, one has to explicitly provide the Fortran runtime libraries
-`FortranRuntime`.  An alternative is to use Flang to link.
+In this case, one has to explicitly provide the Fortran runtime library
+`flang_ty`.  An alternative is to use Flang to link.
 In this case, it may be required to explicitly supply C++ runtime libraries.
 
 On Darwin, the logical root where the system libraries are located (sysroot)
diff --git a/flang/docs/GettingStarted.md b/flang/docs/GettingStarted.md
index eb9049ad607570..9061a00c2de250 100644
--- a/flang/docs/GettingStarted.md
+++ b/flang/docs/GettingStarted.md
@@ -32,8 +32,8 @@ tool.
 
 ### Building flang in tree (bootstrap build)
 Building flang in tree means building flang along with all of the projects on
-which it depends.  These projects include mlir, clang, flang, openmp,
-compiler-rt, and FortranRuntime.  Note that compiler-rt is only needed to access libraries that
+which it depends.  These projects include mlir, clang, flang, openmp, and
+compiler-rt.  Note that compiler-rt is only needed to access libraries that
 support 16 bit floating point numbers.  It's not needed to run the automated
 tests.  You can use several different C++ compilers for most of the build,
 includig GNU and clang.  But building compiler-rt requres using the clang
@@ -82,7 +82,7 @@ cmake \
   -DLLVM_TARGETS_TO_BUILD=host \
   -DLLVM_LIT_ARGS=-v \
   -DLLVM_ENABLE_PROJECTS="clang;mlir;flang;openmp" \
-  -DLLVM_ENABLE_RUNTIMES="compiler-rt;FortranRuntime" \
+  -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang_rt" \
   ../llvm-project/llvm
 
 ninja
@@ -209,15 +209,15 @@ mkdir build_flang_runtime
 cd build_flang_runtime
 
 cmake \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
   -DCMAKE_CUDA_COMPILER=clang \
   -DCMAKE_CUDA_HOST_COMPILER=clang++ \
   ../runtimes/
-make -j`nprocs` FortranRuntime
+make -j`nprocs` flang_rt
 ```
 
 Note that the used version of `clang` must [support](https://releases.llvm.org/16.0.0/tools/clang/docs/ReleaseNotes.html#cuda-support)
@@ -232,8 +232,8 @@ mkdir build_flang_runtime
 cd build_flang_runtime
 
 cmake \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
@@ -241,7 +241,7 @@ cmake \
   -DCMAKE_CUDA_HOST_COMPILER=clang++ \
   ../runtimes/
 
-make -j`nprocs` FortranRuntime
+make -j`nprocs` flang_rt
 ```
 
 Note that `nvcc` might limit support to certain
@@ -260,8 +260,8 @@ build config:
 
 For example:
 ```bash
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
@@ -272,8 +272,8 @@ For example:
 
 Or:
 ```bash
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT=CUDA \
   -DCMAKE_CUDA_ARCHITECTURES=80 \
   -DCMAKE_C_COMPILER=gcc \
   -DCMAKE_CXX_COMPILER=g++ \
@@ -295,14 +295,14 @@ mkdir build_flang_runtime
 cd build_flang_runtime
 
 cmake \
-  -DLLVM_ENABLE_RUNTIMES=FortranRuntime \
-  -DFORTRANRUNTIME_EXPERIMENTAL_OFFLOAD_SUPPORT="OpenMP" \
+  -DLLVM_ENABLE_RUNTIMES=flang_rt \
+  -DFLANG_RT_EXPERIMENTAL_OFFLOAD_SUPPORT="OpenMP" \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
-  -DFORTRANRUNTIME_DEVICE_ARCHITECTURES="all" \
+  -DFLANG_RT_DEVICE_ARCHITECTURES="all" \
   ../runtimes/
 
-make -j`nprocs` FortranRuntime
+make -j`nprocs` flang_rt
 ```
 
 The result of the build is a "device-only" library, i.e. the host
diff --git a/flang/docs/OpenACC-descriptor-management.md b/flang/docs/OpenACC-descriptor-management.md
index 0b5103000d8e7c..215643086fb7d1 100644
--- a/flang/docs/OpenACC-descriptor-management.md
+++ b/flang/docs/OpenACC-descriptor-management.md
@@ -427,7 +427,7 @@ The implementation's behavior may be described as (OpenACC 2.7.2):
 
 All the "is-present" checks and the data actions for the auxiliary pointers must be performed atomically with regards to the present counters bookkeeping.
 
-The API relies on the primitives provided by `liboffload`, so it is provided by a new F18 runtime library, e.g. `FortranOffloadRuntime`, that depends on `FortranRuntime` and `liboffload`.  The F18 driver adds `FortranOffloadRuntime` for linking under `-fopenacc`/`-fopenmp` (and maybe additional switches like `-fopenmp-targets`).
+The API relies on the primitives provided by `liboffload`, so it is provided by a new F18 runtime library, e.g. `FortranOffloadRuntime`, that depends on `flang_rt` and `liboffload`.  The F18 driver adds `FortranOffloadRuntime` for linking under `-fopenacc`/`-fopenmp` (and maybe additional switches like `-fopenmp-targets`).
 
 ## TODOs:
 
diff --git a/flang/docs/ReleaseNotes.md b/flang/docs/ReleaseNotes.md
index 80ebbb5481ba50..347f470452b247 100644
--- a/flang/docs/ReleaseNotes.md
+++ b/flang/docs/ReleaseNotes.md
@@ -36,12 +36,13 @@ page](https://llvm.org/releases/).
 
 ## Build System Changes
 
- * The Fortran Runtime library (libFortranRuntime) has been move to a new
-   top-level directory named "FortranRuntime". It now supports the
-   LLVM_ENABLE_RUNTIMES mechanism to build libFortranRuntime for multiple target
-   triples. libFortranRuntime.a will now be emitted into Clang's per-target
-   resource directory (next to libclang_rt) where it is also found by Flang's
-   driver.
+ * The Fortran Runtime library has been move to a new top-level directory
+   named "flang-rt". The library was also renamed from `libFortranRuntime.a` to
+   `libflang_rt.a`. It now supports the
+   LLVM_ENABLE_RUNTIMES mechanism to build flang-rt for multiple target
+   triples. libflang_rt.a will now be emitted into Clang's per-target
+   resource directory (next to libclang_rt.*.*) where it is also found by
+   Flang's driver.
 
 ## New Issues Found
 
diff --git a/flang/examples/ExternalHelloWorld/CMakeLists.txt b/flang/examples/ExternalHelloWorld/CMakeLists.txt
index 042d4b6238ba45..213fc462ac2b1a 100644
--- a/flang/examples/ExternalHelloWorld/CMakeLists.txt
+++ b/flang/examples/ExternalHelloWorld/CMakeLists.txt
@@ -5,5 +5,5 @@ add_llvm_example(external-hello-world
 
 target_link_libraries(external-hello-world
   PRIVATE
-  FortranRuntime
+  flang_rt
   )
diff --git a/flang/include/flang/Common/README.md b/flang/include/flang/Common/README.md
index a722732fb76407..5203465f7f2fa9 100644
--- a/flang/include/flang/Common/README.md
+++ b/flang/include/flang/Common/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/flang/include/flang/ISO_Fortran_binding.h b/flang/include/flang/ISO_Fortran_binding.h
index 89a10ce69a2ba2..b211bcd98af868 100644
--- a/flang/include/flang/ISO_Fortran_binding.h
+++ b/flang/include/flang/ISO_Fortran_binding.h
@@ -1,3 +1,11 @@
+//===-- include/flang/ISO_Fortran_binding.h ---------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
 /*===-- include/flang/ISO_Fortran_binding.h -----------------------*- C++ -*-===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
@@ -7,14 +15,14 @@
  * ===-----------------------------------------------------------------------===
  */
 
-#ifndef CFI_ISO_FORTRAN_BINDING_H_
-#define CFI_ISO_FORTRAN_BINDING_H_
+#ifndef FORTRAN_ISO_FORTRAN_BINDING_H_
+#define FORTRAN_ISO_FORTRAN_BINDING_H_
 
 /* When this header is included into the compiler and runtime implementations,
  * it does so by means of a wrapper header that establishes namespaces and
  * a macro for extra function attributes (RT_API_ATTRS).
  */
-#ifndef FORTRAN_ISO_FORTRAN_BINDING_WRAPPER_H_
+#ifndef FORTRAN_COMMON_ISO_FORTRAN_BINDING_WRAPPER_H_
 #include <stddef.h>
 #define FORTRAN_ISO_NAMESPACE_
 #endif
@@ -207,4 +215,4 @@ RT_API_ATTRS int CFI_setpointer(
 } // extern "C"
 #endif
 
-#endif /* CFI_ISO_FORTRAN_BINDING_H_ */
+#endif /* FORTRAN_ISO_FORTRAN_BINDING_H_ */
diff --git a/flang/include/flang/Runtime/README.md b/flang/include/flang/Runtime/README.md
index a13a7e23162e98..5203465f7f2fa9 100644
--- a/flang/include/flang/Runtime/README.md
+++ b/flang/include/flang/Runtime/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
diff --git a/flang/include/flang/Testing/README.md b/flang/include/flang/Testing/README.md
index a722732fb76407..5203465f7f2fa9 100644
--- a/flang/include/flang/Testing/README.md
+++ b/flang/include/flang/Testing/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/flang/lib/Common/README.md b/flang/lib/Common/README.md
index a722732fb76407..5203465f7f2fa9 100644
--- a/flang/lib/Common/README.md
+++ b/flang/lib/Common/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/flang/lib/Optimizer/Builder/IntrinsicCall.cpp b/flang/lib/Optimizer/Builder/IntrinsicCall.cpp
index b98ab3e6999655..44c8fba5ee3c66 100644
--- a/flang/lib/Optimizer/Builder/IntrinsicCall.cpp
+++ b/flang/lib/Optimizer/Builder/IntrinsicCall.cpp
@@ -751,7 +751,7 @@ prettyPrintIntrinsicName(fir::FirOpBuilder &builder, mlir::Location loc,
 // Generate a call to the Fortran runtime library providing
 // support for 128-bit float math.
 // On 'LDBL_MANT_DIG == 113' targets the implementation
-// is provided by FortranRuntime, otherwise, it is done via
+// is provided by flang-rt, otherwise, it is done via
 // FortranFloat128Math library. In the latter case the compiler
 // has to be built with FLANG_RUNTIME_F128_MATH_LIB to guarantee
 // proper linking actions in the driver.
diff --git a/flang/lib/Optimizer/Transforms/CufOpConversion.cpp b/flang/lib/Optimizer/Transforms/CufOpConversion.cpp
index d7d321c6b9af3f..68ce3ab7045505 100644
--- a/flang/lib/Optimizer/Transforms/CufOpConversion.cpp
+++ b/flang/lib/Optimizer/Transforms/CufOpConversion.cpp
@@ -1,4 +1,4 @@
-//===-- CufOpConversion.cpp -----------------------------------------------===//
+//===-- lib/Optimizer/Transforms/CufOpConversion.cpp ------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
diff --git a/flang/lib/Testing/CMakeLists.txt b/flang/lib/Testing/CMakeLists.txt
deleted file mode 100644
index d5caada3fb68e8..00000000000000
--- a/flang/lib/Testing/CMakeLists.txt
+++ /dev/null
@@ -1,20 +0,0 @@
-#===-- lib/Testing/CMakeLists.txt ------------------------------------------===#
-#
-# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-# See https://llvm.org/LICENSE.txt for license information.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#
-#===------------------------------------------------------------------------===#
-
-set(public_headers "")
-file(GLOB_RECURSE public_headers
-  "${FLANGRUNTIME_SOURCE_DIR}/lib/Testing/*.h"
-)
-
-add_fortranruntime_library(NonGTestTesting EXCLUDE_FROM_ALL LINK_TO_LLVM
-  testing.cpp
-  fp-testing.cpp
- ADDITIONAL_HEADERS
-   ${public_headers}
-)
-
diff --git a/flang/lib/Testing/README.md b/flang/lib/Testing/README.md
index a722732fb76407..5203465f7f2fa9 100644
--- a/flang/lib/Testing/README.md
+++ b/flang/lib/Testing/README.md
@@ -1,8 +1,8 @@
-Files in this directory are used by Flang (the compiler) and FortranRuntime
+Files in this directory are used by Flang (the compiler) and flang-rt
 (the runtime library for Flang-compiled programs). They must be compatible by
 both. For definitions used only by Flang, consider
 `flang/{lib,include/flang}/Support` instead. For definitions used only by
-FortranRuntime, consider `FortranRuntime/{lib,include/FortranRuntime}/Runtime`.
+the runtime, consider `flang-rt/{lib,include/flang-rt}/flang_rt`.
 
 The requirements for common code include:
 
@@ -23,3 +23,5 @@ The requirements for common code include:
 
  * Global declarations may need to be annotated using definitions from
    `api-attrs.h`.
+
+ * The `Runtime` component is header-only.
diff --git a/FortranRuntime/lib/Runtime/iso_fortran_env_impl.f90 b/flang/module/iso_fortran_env_impl.f90
similarity index 97%
rename from FortranRuntime/lib/Runtime/iso_fortran_env_impl.f90
rename to flang/module/iso_fortran_env_impl.f90
index 1a4da69266c55b..782be81791af2e 100644
--- a/FortranRuntime/lib/Runtime/iso_fortran_env_impl.f90
+++ b/flang/module/iso_fortran_env_impl.f90
@@ -1,4 +1,4 @@
-!===-- lib/Runtime/iso_fortran_env_impl.f90 --------------------------------===!
+!===-- module/iso_fortran_env_impl.f90 --=--------------------------------===!
 !
 ! Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 ! See https://llvm.org/LICENSE.txt for license information.
@@ -8,7 +8,7 @@
 
 ! This MODULE implements part of the ISO_FORTRAN_ENV module file, which
 ! partially requires linkable symbols for some entities defined
-! (e.g., real_kinds).
+! (e.g., real_kinds). Hence, this file is also used by Flang-RT.
 
 module iso_fortran_env_impl
   implicit none
diff --git a/flang/test/Driver/gcc-toolchain-install-dir.f90 b/flang/test/Driver/gcc-toolchain-install-dir.f90
index 5a073b0c517122..d9160e1971250f 100644
--- a/flang/test/Driver/gcc-toolchain-install-dir.f90
+++ b/flang/test/Driver/gcc-toolchain-install-dir.f90
@@ -1,5 +1,5 @@
 !! Test that --gcc-toolchain and --gcc-install-dir options are working as expected.
-!! It does not test cross-compiling (--sysroot), so crtbegin.o, libgcc/compiler-rt, libc, libFortranRuntime, etc. are not supposed to be affected.
+!! It does not test cross-compiling (--sysroot), so crtbegin.o, libgcc/compiler-rt, libc, libflang_rt, etc. are not supposed to be affected.
 !! PREFIX is captured twice because the driver escapes backslashes (occuring in Windows paths) in the -### output, but not on the "Selected GCC installation:" line.
 
 ! RUN: %flang 2>&1 -### -v -o %t %s -no-integrated-as -fuse-ld=ld --target=i386-unknown-linux-gnu --gcc-install-dir=%S/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0 | FileCheck %s --check-prefix=CHECK-I386
diff --git a/flang/test/Driver/linker-flags.f90 b/flang/test/Driver/linker-flags.f90
index fdeb95e4dd97c6..5dc89fe45c8cc0 100644
--- a/flang/test/Driver/linker-flags.f90
+++ b/flang/test/Driver/linker-flags.f90
@@ -33,26 +33,26 @@
 ! SOLARIS-F128NONE-NOT: FortranFloat128Math
 ! UNIX-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
 ! SOLARIS-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "-z" "ignore" "-lquadmath" "-z" "record"
-! UNIX-SAME: "-lFortranRuntime" "-lm"
+! UNIX-SAME: "-lflang_rt" "-lm"
 ! COMPILER-RT: "{{.*}}{{\\|/}}libclang_rt.builtins.a"
 
 ! DARWIN-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! DARWIN-SAME: "[[object_file]]"
 ! DARWIN-F128NONE-NOT: FortranFloat128Math
 ! DARWIN-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
-! DARWIN-SAME: -lFortranRuntime
+! DARWIN-SAME: -lflang_rt
 
 ! HAIKU-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! HAIKU-SAME: "[[object_file]]"
 ! HAIKU-F128NONE-NOT: FortranFloat128Math
 ! HAIKU-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
-! HAIKU-SAME: "-lFortranRuntime"
+! HAIKU-SAME: "-lflang_rt"
 
 ! MINGW-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! MINGW-SAME: "[[object_file]]"
 ! MINGW-F128NONE-NOT: FortranFloat128Math
 ! MINGW-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
-! MINGW-SAME: -lFortranRuntime
+! MINGW-SAME: -lflang_rt
 
 ! NOTE: This also matches lld-link (when CLANG_DEFAULT_LINKER=lld) and
 !       any .exe suffix that is added when resolving to the full path of
diff --git a/flang/test/Driver/msvc-dependent-lib-flags.f90 b/flang/test/Driver/msvc-dependent-lib-flags.f90
index e7fa63548fa840..5e4e6d5952efda 100644
--- a/flang/test/Driver/msvc-dependent-lib-flags.f90
+++ b/flang/test/Driver/msvc-dependent-lib-flags.f90
@@ -6,23 +6,23 @@
 ! MSVC: -fc1
 ! MSVC-SAME: -D_MT
 ! MSVC-SAME: --dependent-lib=libcmt
-! MSVC-SAME: --dependent-lib=FortranRuntime.static.lib
+! MSVC-SAME: --dependent-lib=flang_rt.static.lib
 
 ! MSVC-DEBUG: -fc1
 ! MSVC-DEBUG-SAME: -D_MT
 ! MSVC-DEBUG-SAME: -D_DEBUG
 ! MSVC-DEBUG-SAME: --dependent-lib=libcmtd
-! MSVC-DEBUG-SAME: --dependent-lib=FortranRuntime.static_dbg.lib
+! MSVC-DEBUG-SAME: --dependent-lib=flang_rt.static_dbg.lib
 
 ! MSVC-DLL: -fc1
 ! MSVC-DLL-SAME: -D_MT
 ! MSVC-DLL-SAME: -D_DLL
 ! MSVC-DLL-SAME: --dependent-lib=msvcrt
-! MSVC-DLL-SAME: --dependent-lib=FortranRuntime.dynamic.lib
+! MSVC-DLL-SAME: --dependent-lib=flang_rt.dynamic.lib
 
 ! MSVC-DLL-DEBUG: -fc1
 ! MSVC-DLL-DEBUG-SAME: -D_MT
 ! MSVC-DLL-DEBUG-SAME: -D_DEBUG
 ! MSVC-DLL-DEBUG-SAME: -D_DLL
 ! MSVC-DLL-DEBUG-SAME: --dependent-lib=msvcrtd
-! MSVC-DLL-DEBUG-SAME: --dependent-lib=FortranRuntime.dynamic_dbg.lib
+! MSVC-DLL-DEBUG-SAME: --dependent-lib=flang_rt.dynamic_dbg.lib
diff --git a/flang/tools/f18/CMakeLists.txt b/flang/tools/f18/CMakeLists.txt
index 401c7cc2bdef79..ada258fae8f7a2 100644
--- a/flang/tools/f18/CMakeLists.txt
+++ b/flang/tools/f18/CMakeLists.txt
@@ -54,8 +54,6 @@ if (NOT CMAKE_CROSSCOMPILING)
   foreach(filename ${MODULES})
     set(depends "")
     set(opts "")
-    set(sourcepath "${FLANG_SOURCE_DIR}/module/${filename}.f90")
-    set(modpath "${FLANG_INTRINSIC_MODULES_DIR}/${filename}.mod")
     if(${filename} STREQUAL "__fortran_builtins" OR
        ${filename} STREQUAL "__ppc_types")
     elseif(${filename} STREQUAL "__ppc_intrinsics" OR
@@ -66,9 +64,6 @@ if (NOT CMAKE_CROSSCOMPILING)
       set(depends ${FLANG_INTRINSIC_MODULES_DIR}/__cuda_builtins.mod)
     else()
       set(depends ${FLANG_INTRINSIC_MODULES_DIR}/__fortran_builtins.mod)
-      if(${filename} STREQUAL "iso_fortran_env_impl")
-        set(sourcepath "${FORTRANRUNTIME_SOURCE_DIR}/lib/Runtime/${filename}.f90")
-      endif()
       if(${filename} STREQUAL "iso_fortran_env")
         set(depends ${depends} ${FLANG_INTRINSIC_MODULES_DIR}/iso_fortran_env_impl.mod)
       endif()
@@ -97,27 +92,20 @@ if (NOT CMAKE_CROSSCOMPILING)
       set(decls "-DFLANG_SUPPORT_R16")
     endif()
 
-    # Some modules have an implementation part that needs to be added to the
-    # FortranRuntime library.
     set(compile_with "-fsyntax-only")
     set(object_output "")
     set(include_in_link FALSE)
 
+    set(base ${FLANG_INTRINSIC_MODULES_DIR}/${filename})
     # TODO: We may need to flag this with conditional, in case Flang is built w/o OpenMP support
-    add_custom_command(OUTPUT ${modpath} ${object_output}
+    add_custom_command(OUTPUT ${base}.mod ${object_output}
       COMMAND ${CMAKE_COMMAND} -E make_directory ${FLANG_INTRINSIC_MODULES_DIR}
       COMMAND flang-new ${opts} ${decls} -cpp ${compile_with} -module-dir ${FLANG_INTRINSIC_MODULES_DIR}
-        ${sourcepath}
-      DEPENDS flang-new ${sourcepath} ${FLANG_SOURCE_DIR}/module/__fortran_builtins.f90 ${depends}
+        ${FLANG_SOURCE_DIR}/module/${filename}.f90
+      DEPENDS flang-new ${FLANG_SOURCE_DIR}/module/${filename}.f90 ${FLANG_SOURCE_DIR}/module/__fortran_builtins.f90 ${depends}
     )
-    list(APPEND MODULE_FILES "${modpath}")
-    install(FILES "${modpath}" DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/flang")
-
-    # If a module has been compiled into an object file, add the file to
-    # the link line for the FortranRuntime library.
-    if(include_in_link)
-      list(APPEND module_objects ${object_output})
-    endif()
+    list(APPEND MODULE_FILES ${base}.mod)
+    install(FILES ${base}.mod DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/flang")
   endforeach()
 
   # Special case for omp_lib.mod, because its source comes from openmp/runtime/src/include.
diff --git a/flang/unittests/Common/CMakeLists.txt b/flang/unittests/Common/CMakeLists.txt
index 5b3aebaf5f654a..709a02f5c789c7 100644
--- a/flang/unittests/Common/CMakeLists.txt
+++ b/flang/unittests/Common/CMakeLists.txt
@@ -6,8 +6,8 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_unittest(FlangCommonTests
+add_flangrt_unittest(FlangCommonTests
   FastIntSetTest.cpp
   LINK_LIBS
-    FortranRuntime.unittest
+    flang_rt.unittest
 )
diff --git a/flang/unittests/Decimal/CMakeLists.txt b/flang/unittests/Decimal/CMakeLists.txt
index 033773049680f6..aaa3210aade7e3 100644
--- a/flang/unittests/Decimal/CMakeLists.txt
+++ b/flang/unittests/Decimal/CMakeLists.txt
@@ -6,15 +6,15 @@
 #
 #===------------------------------------------------------------------------===#
 
-add_fortranruntime_nongtest_unittest(quick-sanity-test
+add_flangrt_nongtest_unittest(quick-sanity-test
 quick-sanity-test.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
 
 # This test is not run by default as it takes a long time to execute.
-add_fortranruntime_nongtest_unittest(thorough-test SLOW_TEST
+add_flangrt_nongtest_unittest(thorough-test SLOW_TEST
 thorough-test.cpp
 LINK_LIBS
-  FortranRuntime.unittest
+  flang_rt.unittest
 )
diff --git a/lld/COFF/MinGW.cpp b/lld/COFF/MinGW.cpp
index 74d1ae0615fa6a..ae51bd5fcae62e 100644
--- a/lld/COFF/MinGW.cpp
+++ b/lld/COFF/MinGW.cpp
@@ -50,11 +50,11 @@ AutoExporter::AutoExporter(
       "libclang_rt.profile-x86_64",
       "libc++",
       "libc++abi",
-      "libFortranRuntime",
-      "libFortranRuntime.static",
-      "libFortranRuntime.dynamic",
-      "libFortranRuntime.static_dbg",
-      "libFortranRuntime.dynamic_dbg",
+      "libflang_rt",
+      "libflang_rt.static",
+      "libflang_rt.dynamic",
+      "libflang_rtstatic_dbg",
+      "libflang_rt.dynamic_dbg",
       "libunwind",
       "libmsvcrt",
       "libucrtbase",
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index 70f6f50ee5e11a..60daeaae6613e9 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -149,7 +149,7 @@ endif()
 # As we migrate runtimes to using the bootstrapping build, the set of default runtimes
 # should grow as we remove those runtimes from LLVM_ENABLE_PROJECTS above.
 set(LLVM_DEFAULT_RUNTIMES "libcxx;libcxxabi;libunwind")
-set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload;FortranRuntime")
+set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload;flang-rt")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all")
diff --git a/llvm/projects/CMakeLists.txt b/llvm/projects/CMakeLists.txt
index d8808bc79f0129..f254cf10806d75 100644
--- a/llvm/projects/CMakeLists.txt
+++ b/llvm/projects/CMakeLists.txt
@@ -12,7 +12,7 @@ foreach(entry ${entries})
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/test-suite) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/openmp) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/cross-project-tests) AND
-       (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/FortranRuntime))
+       (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/flang-rt))
       get_filename_component(entry_name "${entry}" NAME)
       add_llvm_external_project(${entry_name})
     endif()
@@ -38,7 +38,7 @@ if(${LLVM_BUILD_RUNTIME})
   if(NOT LLVM_BUILD_EXTERNAL_COMPILER_RT)
     add_llvm_external_project(compiler-rt)
   endif()
-  add_llvm_external_project(FortranRuntime)
+  add_llvm_external_project(flang-rt)
 endif()
 
 add_llvm_external_project(dragonegg)
diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index 80f1cf5d6b6ea6..79abe65b4c17d6 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -280,8 +280,8 @@ function(runtime_default_target)
                                       ${ARG_CMAKE_ARGS}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                                                 LLVM_USE_LINKER
-                                                CUDA # For runtimes that may look for the CUDA SDK (libc, offload)
-                                                FLANG_RUNTIME # Shared between Flang and FortranRuntime
+                                                CUDA # For runtimes that may look for the CUDA SDK (libc, offload, flang-rt)
+                                                FLANG_RUNTIME # Shared between Flang and Flang-RT
                                                 ${ARG_PREFIXES}
                            EXTRA_TARGETS ${extra_targets}
                                          ${test_targets}
@@ -573,7 +573,7 @@ if(build_runtimes)
   if(LLVM_LIBC_FULL_BUILD)
     list(APPEND extra_cmake_args "-DLLVM_LIBC_FULL_BUILD=ON")
   endif()
-  if("FortranRuntime" IN_LIST LLVM_ENABLE_RUNTIMES)
+  if("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
     set(enable_fortran ENABLE_FORTRAN)
   endif ()
 
diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
index 2a7798fd60af42..1dc42ddc27d2d0 100644
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -23,8 +23,8 @@ list(INSERT CMAKE_MODULE_PATH 0
 
 # We order libraries to mirror roughly how they are layered, except that compiler-rt can depend
 # on libc++, so we put it after.
-set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;offload;FortranRuntime")
-set(LLVM_SUPPORTED_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc")
+set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;offload")
+set(LLVM_SUPPORTED_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc;flang-rt")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all" )