diff --git a/cadCAD/types.py b/cadCAD/types.py
new file mode 100644
index 00000000..5b47964e
--- /dev/null
+++ b/cadCAD/types.py
@@ -0,0 +1,18 @@
+from typing import TypedDict, Callable, Union, Dict, List, Tuple
+
+State = Dict[str, object]
+Parameters = Dict[str, object]
+Substep = int
+StateHistory = List[List[State]]
+PolicyOutput = Dict[str, object]
+StateVariable = object
+
+PolicyFunction = Callable[[Parameters, Substep, StateHistory, State], PolicyOutput]
+StateUpdateFunction = Callable[[Parameters, Substep, StateHistory, State, PolicyOutput], Tuple[str, StateVariable]]
+
+class StateUpdateBlock(TypedDict):
+    policies: Dict[str, PolicyFunction]
+    variables: Dict[str, StateUpdateFunction]
+
+
+StateUpdateBlocks = List[StateUpdateBlock]