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+# Lighthouse Interop Guide
+
+This guide is intended for other Ethereum 2.0 client developers performing
+inter-operability testing with Lighthouse.
+
+To allow for faster iteration cycles without the "merging to master" overhead,
+we will use the [`interop`](https://github.com/sigp/lighthouse/tree/interop)
+branch of [sigp/lighthouse](https://github.com/sigp/lighthouse/tree/interop)
+for September 2019 interop.  **Please use ensure you `git checkout interop`
+after cloning the repo.**
+
+## Environment
+
+All that is required for inter-op is a built and tested [development
+environment](setup). When lighthouse boots, it will create the following
+directories:
+
+- `~/.lighthouse`: database and configuration for the beacon node.
+- `~/.lighthouse-validator`: database and configuration for the validator
+	client.
+
+After building the binaries with `cargo build --release --all`, there will be a
+`target/release` directory in the root of the Lighthouse repository. This is
+where the `beacon_node` and `validator_client` binaries are located.
+
+## Interop Procedure
+
+The following scenarios are documented:
+
+- [Starting a "quick-start" beacon node](#quick-start-beacon-node) from a
+    `(validator_count, genesis)` tuple.
+- [Starting a validator client](#validator-client) with `n` interop keypairs.
+- [Starting a node from a genesis state file](#starting-from-a-genesis-file).
+- [Exporting a genesis state file](#exporting-a-genesis-file) from a running Lighthouse
+	node.
+
+First, setup a Lighthouse development environment and navigate to the
+`target/release` directory (this is where the binaries are located).
+
+#### Quick-start Beacon Node
+
+
+To start the node (each time creating a fresh database and configuration in
+`~/.lighthouse`), use:
+
+```
+$ ./beacon_node testnet -f quick 8 1567222226
+```
+
+>This method conforms the ["Quick-start
+genesis"](https://github.com/ethereum/eth2.0-pm/tree/6e41fcf383ebeb5125938850d8e9b4e9888389b4/interop/mocked_start#quick-start-genesis)
+method in the `ethereum/eth2.0-pm` repository.
+>
+> The `-f` flag ignores any existing database or configuration, backing them up
+before re-initializing. `8` is the validator count and `1567222226` is the
+genesis time.
+>
+> See `$ ./beacon_node testnet quick --help` for more configuration options.
+
+#### Validator Client
+
+**TODO**
+
+#### Starting from a genesis file
+
+**TODO**
+
+#### Exporting a genesis file
+
+**TODO**