diff --git a/book/src/interop.md b/book/src/interop.md
index 79d4a1376..ea00c4ce8 100644
--- a/book/src/interop.md
+++ b/book/src/interop.md
@@ -46,20 +46,36 @@ To start the node (each time creating a fresh database and configuration in
 ```
 $ ./beacon_node testnet -f quick 8 1567222226
 ```
-
->This method conforms the ["Quick-start
+> Notes:
+>
+> - 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.
+> - 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**
+Start the validator client with:
+
+```
+$ ./validator_client testnet -b insecure 0 8
+```
+> Notes:
+>
+> - The `-b` flag means the validator client will "bootstrap" specs and config
+>   from the beacon node.
+> - The `insecure` command means the [interop
+>   keypairs](https://github.com/ethereum/eth2.0-pm/tree/6e41fcf383ebeb5125938850d8e9b4e9888389b4/interop/mocked_start#pubkeyprivkey-generation)
+>   will be used.
+> - The `0 8` indicates that this validator client should manage 8 validators,
+>   starting at validator 0 (the first deposited validator).
+> - The validator client will try to connect to the beacon node at `localhost`.
+>   See `--help` to configure that address and other features.
+> - The validator client will operate very loosely in `testnet` mode, happily
+>   swapping between chains and creating double-votes.
 
 #### Starting from a genesis file
 
diff --git a/book/src/testnets.md b/book/src/testnets.md
index c07797ba0..bf41e455d 100644
--- a/book/src/testnets.md
+++ b/book/src/testnets.md
@@ -12,7 +12,7 @@ Setup a development environment, build the project and navigate to the
 `target/release` directory.
 
 1. Start the first node: `$ ./beacon_node testnet -f recent 8`
-1. Start a validator client: **TODO**
+1. Start a validator client: `$ ./validator_client testnet -b insecure 0 8`
 1. Start another node `$ ./beacon_node -b 10 testnet -f bootstrap http://localhost:5052`
 
 _Repeat #3 to add more nodes._
@@ -30,16 +30,32 @@ Start a new node (creating a fresh database and configuration in `~/.lighthouse`
 $ ./beacon_node testnet -f recent 8
 ```
 
-> The `-f` flag ignores any existing database or configuration, backing them up
-before re-initializing. `8` is number of validators with deposits in the
-genesis state.
+> Notes:
 >
-> See `$ ./beacon_node testnet recent --help` for more configuration options,
-including `minimal`/`mainnet` specification.
+> - The `-f` flag ignores any existing database or configuration, backing them
+>   up before re-initializing.
+> - `8` is number of validators with deposits in the genesis state.
+> - See `$ ./beacon_node testnet recent --help` for more configuration options,
+>   including `minimal`/`mainnet` specification.
 
 ## Starting the Validator Client
 
-**TODO**
+In a new terminal window, start the validator client with:
+
+```
+$ ./validator_client testnet -b insecure 0 8
+```
+
+> Notes:
+>
+> - The `-b` flag means the validator client will "bootstrap" specs and config
+>   from the beacon node.
+> - The `insecure` command uses predictable, well-known private keys. Since
+>   this is just a local testnet, these are fine.
+> - The `0 8` indicates that this validator client should manage 8 validators,
+>   starting at validator 0 (the first deposited validator).
+> - The validator client will try to connect to the beacon node at `localhost`.
+>   See `--help` to configure that address and other features.
 
 ## Adding another Beacon Node
 
@@ -53,12 +69,12 @@ In a new terminal terminal, run:
 $ ./beacon_node -b 10 testnet -r bootstrap http://localhost:5052
 ```
 
-> The `-b` (or `--port-bump`) increases all the listening TCP/UDP ports of the
-new node to `10` higher. Your first node's HTTP server was at TCP `5052` but
-this one will be at `5062`.
+> Notes:
 >
-> The `-r` flag creates a new data directory in your home with a random string
-appended, to avoid conflicting with any other running node.
->
-> The HTTP address is the API of the first node. The new node will download
-configuration via HTTP before starting sync via libp2p.
+> - The `-b` (or `--port-bump`) increases all the listening TCP/UDP ports of
+>   the new node to `10` higher. Your first node's HTTP server was at TCP
+>   `5052` but this one will be at `5062`.
+> - The `-r` flag creates a new data directory in your home with a random
+>   string appended, to avoid conflicting with any other running node.
+> - The HTTP address is the API of the first node. The new node will download
+>   configuration via HTTP before starting sync via libp2p.