diff --git a/README.md b/README.md
index a252a10..1f81cea 100644
--- a/README.md
+++ b/README.md
@@ -18,3 +18,38 @@ Copy INTERACTION Dataset files:
 The INTERACTION dataset contains a two folders which should be copied into a folder called `./InteractionSimulator/datasets`: 
   - the contents of `recorded_trackfiles` should be copied to `./InteractionSimulator/datasets/trackfiles`
   - the contents of `maps` should be copied to `./InteractionSimulator/datasets/maps`
+
+# Package Structure
+```
+InteractionImitation
+|- demos
+|- algorithms
+   |- BC
+   |- AdVIL
+|- nets
+   |- Encoder
+   |- DeepSet
+   |- Decoder
+|- policies
+|- discriminators
+|- demo_generators
+```
+
+## Type Definitions
+```
+Demo: List[Trajectory]
+Trajectory: List[Tuple[Observation, Action]] # single expert
+Observation: Dict[
+  'own_state': [x, y, v, psi, psidot],
+  'relative_states': List[[xr, yr, vr, psir, psidotr]],
+  'own_path': List[[xr, yr]], # fixed length, constant dt
+  'map': Map, # relative
+]
+Action: Range[0, 1]
+Policy: Union[
+  Callable[[Observation], Action],
+  Callable[[Observation, Action], probability],
+]
+Discriminator: Callable[[Observation, Action], value]
+Map: Dictionary[...]
+```