diff --git a/automotive/vehicle/README.md b/automotive/vehicle/README.md
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+# Vehicle Hardware Abstraction Layer (VHAL)
+---
+
+This directory stores the VHAL interface definition and VHAL reference
+implementation.
+
+## 2.0 (deprecated)
+
+HIDL based VHAL interface and reference implementation. 
+
+## aidl
+
+AIDL based VHAL interfadce and reference implementation.
+
+## proto
+
+Protobuf used to pass message between emulator VHAL and emulator.
+
+## tools
+
+Dev tools related to VHAL.
+
+## vts
+
+VTS test for VHAL. The VTS test works for both AIDL and HIDL VHAL
+implementation. Vendor implementation of VHAL must passes VTS.
diff --git a/automotive/vehicle/aidl/README.md b/automotive/vehicle/aidl/README.md
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+# AIDL Vehicle Hardware Abstraction Layer (VHAL)
+---
+
+This directory stores the AIDL VHAL interface and reference implementation.
+
+## aidl_api
+
+Auto-generated current and previous versions of AIDL VHAL api.
+
+## aidl_test
+
+Contains a test to test that all HIDL VHAL properties are supported in
+AIDL VHAL.
+
+## android
+
+Contains AIDL VHAL interface definition. The main interface file is
+`android/hardware/automotive/vehicle/IVehicle.aidl`.
+
+## impl
+
+Reference implementation for AIDL VHAL and useful libraries for implementing
+vendor AIDL VHAL.
diff --git a/automotive/vehicle/aidl/impl/README.md b/automotive/vehicle/aidl/impl/README.md
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+# AIDL VHAL libraries and reference implementation.
+---
+
+This directory stores the libraries useful for implementing vendor AIDL VHAL.
+This directory also stores a reference fake implementation for AIDL VHAL.
+
+## default_config
+
+Stores the default vehicle property configurations for reference vehicle HAL.
+Vendor implementation could copy this library but must update the configuration
+to meet their own requirements, e.g. enable or disable certain properties or
+update the initial value for certain properties.
+
+##	fake_impl
+
+Contains libraries used specifically for the fake reference VHAL implementation.
+These libraries are for test only and must not be directly used for vendor
+VHAL implementation.
+
+These libraries contain test-spcific logic and must not run directly on a real
+vehicle.
+
+## grpc
+
+Stores code for GRPC based VHAL implementation.
+
+## hardware
+
+Defines an interface `IVehicleHardware.h` which vendor must implement for
+vehicle-specific logic if they want to follow our reference VHAL design.
+
+## proto
+
+Stores Some protobuf files translated from AIDL VHAL interface types. These
+files are used in GRPC VHAL implementation.
+
+## utils
+
+Defines a library `VehicleHalUtils` which provides useful utility functions for
+VHAL implementation. Vendor VHAL could use this library.
+
+## vhal
+
+Defines a library `DefaultVehicleHal` which provides generic logic for all VHAL
+implementations (including reference VHAL). Vendor VHAL implementation could
+use this library, along with their own implementation for `IVehicleHardware`
+interface.
+
+Also defines a binary `android.hardware.automotive.vehicle@V1-default-service`
+which is the reference VHAL implementation. It implements `IVehicle.aidl`
+interface. It uses `DefaultVehicleHal`, along with `FakeVehicleHardware`
+(in fake_impl). It simulates the vehicle bus interaction by using an
+in-memory map. Meaning that all properties (except for some special ones) are
+just written into a hash map and read from a hash map without relying on any
+hardware. As a result, the reference implementation can run on emulator or
+any host environment.
+
+Vendor must not directly use the reference implementation for a real vehicle.
\ No newline at end of file
diff --git a/automotive/vehicle/aidl/impl/fake_impl/README.md b/automotive/vehicle/aidl/impl/fake_impl/README.md
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+# Fake reference AIDL VHAL implementation libraries
+---
+
+This directory stores libraries for implementing a fake reference AIDL VHAL.
+
+WARNING: All the libraries here are for TEST ONLY.
+
+## GeneratorHub
+
+Defines a library `FakeVehicleHalValueGenerators` that could generate fake
+vehicle property values for testing.
+
+## hardware
+
+Defines a fake implementation for device-specifc interface `IVehicleHardware`:
+`FakeVehicleHardware`. This implementation uses a in-memory map for storing
+property values and does not communicate with or depending on any specific
+vehicle bus.
+
+## obd2frame
+
+Defines a library `FakeObd2Frame` that generates fake OBD2 frame for OBD2
+properties.
+
+## userhal
+
+Defines a library `FakeUserHal` that emulates a real User HAL behavior by
+parsing debug commands.
diff --git a/automotive/vehicle/aidl/impl/utils/README.md b/automotive/vehicle/aidl/impl/utils/README.md
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+# Utility classes for VHAL implementation
+---
+
+This directory stores utility classes for VHAL implementation. Vendor
+implementation could use utility classes from `common` folder in their
+VHAL implementation.
+
+## common
+
+Defines common utility libraries.
+
+### ConcurrentQueue
+
+Provides a thread-safe concurrent queue object. Useful for adding object to
+a queue in one thread (usually binder thread) and handle the objects in a
+separate handler thread.
+
+### ParcelableUtils
+
+Provides functions to convert between a regular parcelable and a
+`LargeParcelabe`.
+
+A `LargeParcelable` is a parcelable that marshals the payload
+into a shared memory file if the payload is too large to pass across binder.
+It is used to pass large data across binder. Before sending the data, VHAL
+impl should convert a regular parcelabe to a `LargeParcelable`. After receving
+data, VHAL impl should convert a `LargeParcelable` back to regular parcelabe.
+
+### PendingRequestPool
+
+Defines A class for managing pending requests and automatically call timeout
+callback if the request timed-out.
+
+### PropertyUtils
+
+Defines some useful constants.
+
+### RecurrentTimer
+
+Defines a thread-safe recurrent timer that can call a function periodically.
+
+### VehicleHalTypes
+
+Provides a header file that includes many commonly used header files. Useful
+when you are using multiple types defined in VHAL interface.
+
+### VehicleObjectPool
+
+Defines a reusable in-memory pool for `VehiclePropValue`.
+
+### VehiclePropertyStore
+
+Defines an in-memory map for storing vehicle properties. Allows easier insert,
+delete and lookup.
+
+### VehicleUtils
+
+Defines many useful utility functions.
+
+## test
+
+Defines utility libraries for test only.