diff --git a/validator_client/src/block_producer/grpc.rs b/validator_client/src/block_producer/grpc.rs
index 4032d49f3..f3156ab9f 100644
--- a/validator_client/src/block_producer/grpc.rs
+++ b/validator_client/src/block_producer/grpc.rs
@@ -7,6 +7,10 @@ use ssz::{ssz_encode, Decodable};
 use types::{BeaconBlock, BeaconBlockBody, Hash256, Signature};
 
 impl BeaconNode for BeaconBlockServiceClient {
+    /// Request a Beacon Node (BN) to produce a new block at the supplied slot.
+    ///
+    /// Returns `None` if it is not possible to produce at the supplied slot. For example, if the
+    /// BN is unable to find a parent block.
     fn produce_beacon_block(&self, slot: u64) -> Result<Option<BeaconBlock>, BeaconNodeError> {
         let mut req = ProduceBeaconBlockRequest::new();
         req.set_slot(slot);
@@ -42,6 +46,10 @@ impl BeaconNode for BeaconBlockServiceClient {
         }
     }
 
+    /// Request a Beacon Node (BN) to publish a block.
+    ///
+    /// Generally, this will be called after a `produce_beacon_block` call with a block that has
+    /// been completed (signed) by the validator client.
     fn publish_beacon_block(&self, block: BeaconBlock) -> Result<bool, BeaconNodeError> {
         let mut req = PublishBeaconBlockRequest::new();
 
diff --git a/validator_client/src/block_producer/mod.rs b/validator_client/src/block_producer/mod.rs
index aa4c088f3..f3cd0199b 100644
--- a/validator_client/src/block_producer/mod.rs
+++ b/validator_client/src/block_producer/mod.rs
@@ -15,11 +15,17 @@ pub use self::service::BlockProducerService;
 
 #[derive(Debug, PartialEq)]
 pub enum PollOutcome {
+    /// A new block was produced.
     BlockProduced(u64),
+    /// A block was not produced as it would have been slashable.
     SlashableBlockNotProduced(u64),
+    /// The validator duties did not require a block to be produced.
     BlockProductionNotRequired(u64),
+    /// The duties for the present epoch were not found.
     ProducerDutiesUnknown(u64),
+    /// The slot has already been processed, execution was skipped.
     SlotAlreadyProcessed(u64),
+    /// The Beacon Node was unable to produce a block at that slot.
     BeaconNodeUnableToProduceBlock(u64),
 }
 
@@ -33,6 +39,12 @@ pub enum Error {
     BeaconNodeError(BeaconNodeError),
 }
 
+/// A polling state machine which performs block production duties, based upon some epoch duties
+/// (`EpochDutiesMap`) and a concept of time (`SlotClock`).
+///
+/// Ensures that messages are not slashable.
+///
+/// Relies upon an external service to keep the `EpochDutiesMap` updated.
 pub struct BlockProducer<T: SlotClock, U: BeaconNode> {
     pub last_processed_slot: u64,
     spec: Arc<ChainSpec>,
@@ -42,6 +54,7 @@ pub struct BlockProducer<T: SlotClock, U: BeaconNode> {
 }
 
 impl<T: SlotClock, U: BeaconNode> BlockProducer<T, U> {
+    /// Returns a new instance where `last_processed_slot == 0`.
     pub fn new(
         spec: Arc<ChainSpec>,
         epoch_map: Arc<RwLock<EpochDutiesMap>>,
@@ -97,6 +110,16 @@ impl<T: SlotClock, U: BeaconNode> BlockProducer<T, U> {
         }
     }
 
+    /// Produce a block at some slot.
+    ///
+    /// Assumes that a block is required at this slot (does not check the duties).
+    ///
+    /// Ensures the message is not slashable.
+    ///
+    /// !!! UNSAFE !!!
+    ///
+    /// The slash-protection code is not yet implemented. There is zero protection against
+    /// slashing.
     fn produce_block(&mut self, slot: u64) -> Result<PollOutcome, Error> {
         if let Some(block) = self.beacon_node.produce_beacon_block(slot)? {
             if self.safe_to_produce(&block) {
@@ -111,19 +134,36 @@ impl<T: SlotClock, U: BeaconNode> BlockProducer<T, U> {
         }
     }
 
+    /// Consumes a block, returning that block signed by the validators private key.
+    ///
+    /// Important: this function will not check to ensure the block is not slashable. This must be
+    /// done upstream.
     fn sign_block(&mut self, block: BeaconBlock) -> BeaconBlock {
         // TODO: sign the block
+        // https://github.com/sigp/lighthouse/issues/160
         self.store_produce(&block);
         block
     }
 
+    /// Returns `true` if signing a block is safe (non-slashable).
+    ///
+    /// !!! UNSAFE !!!
+    ///
+    /// Important: this function is presently stubbed-out. It provides ZERO SAFETY.
     fn safe_to_produce(&self, _block: &BeaconBlock) -> bool {
         // TODO: ensure the producer doesn't produce slashable blocks.
+        // https://github.com/sigp/lighthouse/issues/160
         true
     }
 
+    /// Record that a block was produced so that slashable votes may not be made in the future.
+    ///
+    /// !!! UNSAFE !!!
+    ///
+    /// Important: this function is presently stubbed-out. It provides ZERO SAFETY.
     fn store_produce(&mut self, _block: &BeaconBlock) {
         // TODO: record this block production to prevent future slashings.
+        // https://github.com/sigp/lighthouse/issues/160
     }
 }
 
@@ -142,6 +182,7 @@ mod tests {
     use types::test_utils::{SeedableRng, TestRandom, XorShiftRng};
 
     // TODO: implement more thorough testing.
+    // https://github.com/sigp/lighthouse/issues/160
     //
     // These tests should serve as a good example for future tests.
 
diff --git a/validator_client/src/block_producer/service.rs b/validator_client/src/block_producer/service.rs
index 222e54d47..ffdb33029 100644
--- a/validator_client/src/block_producer/service.rs
+++ b/validator_client/src/block_producer/service.rs
@@ -10,6 +10,9 @@ pub struct BlockProducerService<T: SlotClock, U: BeaconNode> {
 }
 
 impl<T: SlotClock, U: BeaconNode> BlockProducerService<T, U> {
+    /// Run a loop which polls the block producer each `poll_interval_millis` millseconds.
+    ///
+    /// Logs the results of the polls.
     pub fn run(&mut self) {
         loop {
             match self.block_producer.poll() {
diff --git a/validator_client/src/block_producer/test_node.rs b/validator_client/src/block_producer/test_node.rs
index 36d47e3c3..e99613e8f 100644
--- a/validator_client/src/block_producer/test_node.rs
+++ b/validator_client/src/block_producer/test_node.rs
@@ -5,6 +5,7 @@ use types::BeaconBlock;
 type ProduceResult = Result<Option<BeaconBlock>, BeaconNodeError>;
 type PublishResult = Result<bool, BeaconNodeError>;
 
+/// A test-only struct used to simulate a Beacon Node.
 #[derive(Default)]
 pub struct TestBeaconNode {
     pub produce_input: RwLock<Option<u64>>,
@@ -14,16 +15,19 @@ pub struct TestBeaconNode {
 }
 
 impl TestBeaconNode {
+    /// Set the result to be returned when `produce_beacon_block` is called.
     pub fn set_next_produce_result(&self, result: ProduceResult) {
         *self.produce_result.write().unwrap() = Some(result);
     }
 
+    /// Set the result to be returned when `publish_beacon_block` is called.
     pub fn set_next_publish_result(&self, result: PublishResult) {
         *self.publish_result.write().unwrap() = Some(result);
     }
 }
 
 impl BeaconNode for TestBeaconNode {
+    /// Returns the value specified by the `set_next_produce_result`.
     fn produce_beacon_block(&self, slot: u64) -> ProduceResult {
         *self.produce_input.write().unwrap() = Some(slot);
         match *self.produce_result.read().unwrap() {
@@ -32,6 +36,7 @@ impl BeaconNode for TestBeaconNode {
         }
     }
 
+    /// Returns the value specified by the `set_next_publish_result`.
     fn publish_beacon_block(&self, block: BeaconBlock) -> PublishResult {
         *self.publish_input.write().unwrap() = Some(block);
         match *self.publish_result.read().unwrap() {
diff --git a/validator_client/src/block_producer/traits.rs b/validator_client/src/block_producer/traits.rs
index aaae031ec..be1c73bda 100644
--- a/validator_client/src/block_producer/traits.rs
+++ b/validator_client/src/block_producer/traits.rs
@@ -6,7 +6,14 @@ pub enum BeaconNodeError {
     DecodeFailure,
 }
 
+/// Defines the methods required to produce and publish blocks on a Beacon Node.
 pub trait BeaconNode: Send + Sync {
+    /// Request that the node produces a block.
+    ///
+    /// Returns Ok(None) if the Beacon Node is unable to produce at the given slot.
     fn produce_beacon_block(&self, slot: u64) -> Result<Option<BeaconBlock>, BeaconNodeError>;
+    /// Request that the node publishes a block.
+    ///
+    /// Returns `true` if the publish was sucessful.
     fn publish_beacon_block(&self, block: BeaconBlock) -> Result<bool, BeaconNodeError>;
 }
diff --git a/validator_client/src/config.rs b/validator_client/src/config.rs
index 4b646074d..104a4bbe6 100644
--- a/validator_client/src/config.rs
+++ b/validator_client/src/config.rs
@@ -11,7 +11,7 @@ pub struct ClientConfig {
 const DEFAULT_LIGHTHOUSE_DIR: &str = ".lighthouse-validators";
 
 impl ClientConfig {
-    /// Build a new lighthouse configuration from defaults.
+    /// Build a new configuration from defaults.
     pub fn default() -> Self {
         let data_dir = {
             let home = dirs::home_dir().expect("Unable to determine home dir.");
diff --git a/validator_client/src/duties/grpc.rs b/validator_client/src/duties/grpc.rs
index 7b4e1e617..b4a2fac51 100644
--- a/validator_client/src/duties/grpc.rs
+++ b/validator_client/src/duties/grpc.rs
@@ -6,6 +6,12 @@ use ssz::ssz_encode;
 use types::PublicKey;
 
 impl BeaconNode for ValidatorServiceClient {
+    /// Request the shuffling from the Beacon Node (BN).
+    ///
+    /// As this function takes a `PublicKey`, it will first attempt to resolve the public key into
+    /// a validator index, then call the BN for production/attestation duties.
+    ///
+    /// Note: presently only block production information is returned.
     fn request_shuffling(
         &self,
         epoch: u64,
diff --git a/validator_client/src/duties/mod.rs b/validator_client/src/duties/mod.rs
index e8438b3db..4656715ba 100644
--- a/validator_client/src/duties/mod.rs
+++ b/validator_client/src/duties/mod.rs
@@ -13,6 +13,11 @@ use std::sync::{Arc, RwLock};
 
 pub use self::service::DutiesManagerService;
 
+/// The information required for a validator to propose and attest during some epoch.
+///
+/// Generally obtained from a Beacon Node, this information contains the validators canonical index
+/// (thier sequence in the global validator induction process) and the "shuffling" for that index
+/// for some epoch.
 #[derive(Debug, PartialEq, Clone, Copy, Default)]
 pub struct EpochDuties {
     pub validator_index: u64,
@@ -21,6 +26,8 @@ pub struct EpochDuties {
 }
 
 impl EpochDuties {
+    /// Returns `true` if the supplied `slot` is a slot in which the validator should produce a
+    /// block.
     pub fn is_block_production_slot(&self, slot: u64) -> bool {
         match self.block_production_slot {
             Some(s) if s == slot => true,
@@ -29,13 +36,20 @@ impl EpochDuties {
     }
 }
 
+/// Maps an `epoch` to some `EpochDuties` for a single validator.
 pub type EpochDutiesMap = HashMap<u64, EpochDuties>;
 
 #[derive(Debug, PartialEq, Clone, Copy)]
 pub enum PollOutcome {
+    /// The `EpochDuties` were not updated during this poll.
     NoChange(u64),
+    /// The `EpochDuties` for the `epoch` were previously unknown, but obtained in the poll.
     NewDuties(u64, EpochDuties),
+    /// New `EpochDuties` were obtained, different to those which were previously known. This is
+    /// likely to be the result of chain re-organisation.
     DutiesChanged(u64, EpochDuties),
+    /// The Beacon Node was unable to return the duties as the validator is unknown, or the
+    /// shuffling for the epoch is unknown.
     UnknownValidatorOrEpoch(u64),
 }
 
@@ -49,8 +63,13 @@ pub enum Error {
     BeaconNodeError(BeaconNodeError),
 }
 
+/// A polling state machine which ensures the latest `EpochDuties` are obtained from the Beacon
+/// Node.
+///
+/// There is a single `DutiesManager` per validator instance.
 pub struct DutiesManager<T: SlotClock, U: BeaconNode> {
     pub duties_map: Arc<RwLock<EpochDutiesMap>>,
+    /// The validator's public key.
     pub pubkey: PublicKey,
     pub spec: Arc<ChainSpec>,
     pub slot_clock: Arc<RwLock<T>>,
@@ -58,6 +77,10 @@ pub struct DutiesManager<T: SlotClock, U: BeaconNode> {
 }
 
 impl<T: SlotClock, U: BeaconNode> DutiesManager<T, U> {
+    /// Poll the Beacon Node for `EpochDuties`.
+    ///
+    /// The present `epoch` will be learned from the supplied `SlotClock`. In production this will
+    /// be a wall-clock (e.g., system time, remote server time, etc.).
     pub fn poll(&self) -> Result<PollOutcome, Error> {
         let slot = self
             .slot_clock
@@ -109,6 +132,7 @@ mod tests {
     use slot_clock::TestingSlotClock;
 
     // TODO: implement more thorough testing.
+    // https://github.com/sigp/lighthouse/issues/160
     //
     // These tests should serve as a good example for future tests.
 
diff --git a/validator_client/src/duties/service.rs b/validator_client/src/duties/service.rs
index 401b7dddd..bdb6faefa 100644
--- a/validator_client/src/duties/service.rs
+++ b/validator_client/src/duties/service.rs
@@ -11,6 +11,9 @@ pub struct DutiesManagerService<T: SlotClock, U: BeaconNode> {
 }
 
 impl<T: SlotClock, U: BeaconNode> DutiesManagerService<T, U> {
+    /// Run a loop which polls the manager each `poll_interval_millis` milliseconds.
+    ///
+    /// Logs the results of the polls.
     pub fn run(&mut self) {
         loop {
             match self.manager.poll() {
diff --git a/validator_client/src/duties/test_node.rs b/validator_client/src/duties/test_node.rs
index 4ec002224..2b1d65172 100644
--- a/validator_client/src/duties/test_node.rs
+++ b/validator_client/src/duties/test_node.rs
@@ -5,6 +5,7 @@ use std::sync::RwLock;
 
 type ShufflingResult = Result<Option<EpochDuties>, BeaconNodeError>;
 
+/// A test-only struct used to simulate a Beacon Node.
 #[derive(Default)]
 pub struct TestBeaconNode {
     pub request_shuffling_input: RwLock<Option<(u64, PublicKey)>>,
@@ -12,12 +13,14 @@ pub struct TestBeaconNode {
 }
 
 impl TestBeaconNode {
+    /// Set the result to be returned when `request_shuffling` is called.
     pub fn set_next_shuffling_result(&self, result: ShufflingResult) {
         *self.request_shuffling_result.write().unwrap() = Some(result);
     }
 }
 
 impl BeaconNode for TestBeaconNode {
+    /// Returns the value specified by the `set_next_shuffling_result`.
     fn request_shuffling(&self, epoch: u64, public_key: &PublicKey) -> ShufflingResult {
         *self.request_shuffling_input.write().unwrap() = Some((epoch, public_key.clone()));
         match *self.request_shuffling_result.read().unwrap() {
diff --git a/validator_client/src/duties/traits.rs b/validator_client/src/duties/traits.rs
index 14c2adf95..38d61f967 100644
--- a/validator_client/src/duties/traits.rs
+++ b/validator_client/src/duties/traits.rs
@@ -6,7 +6,11 @@ pub enum BeaconNodeError {
     RemoteFailure(String),
 }
 
+/// Defines the methods required to obtain a validators shuffling from a Beacon Node.
 pub trait BeaconNode: Send + Sync {
+    /// Get the shuffling for the given epoch and public key.
+    ///
+    /// Returns Ok(None) if the public key is unknown, or the shuffling for that epoch is unknown.
     fn request_shuffling(
         &self,
         epoch: u64,
diff --git a/validator_client/src/main.rs b/validator_client/src/main.rs
index a52ffe124..bbbc0b4c3 100644
--- a/validator_client/src/main.rs
+++ b/validator_client/src/main.rs
@@ -83,6 +83,7 @@ fn main() {
     // Ethereum
     //
     // TODO: Permit loading a custom spec from file.
+    // https://github.com/sigp/lighthouse/issues/160
     let spec = Arc::new(ChainSpec::foundation());
 
     // Clock for determining the present slot.
@@ -99,13 +100,16 @@ fn main() {
     /*
      * Start threads.
      */
-    let keypairs = vec![Keypair::random()];
     let mut threads = vec![];
+    // TODO: keypairs are randomly generated; they should be loaded from a file or generated.
+    // https://github.com/sigp/lighthouse/issues/160
+    let keypairs = vec![Keypair::random()];
 
     for keypair in keypairs {
         info!(log, "Starting validator services"; "validator" => keypair.pk.concatenated_hex_id());
         let duties_map = Arc::new(RwLock::new(EpochDutiesMap::new()));
 
+        // Spawn a new thread to maintain the validator's `EpochDuties`.
         let duties_manager_thread = {
             let spec = spec.clone();
             let duties_map = duties_map.clone();
@@ -131,6 +135,7 @@ fn main() {
             })
         };
 
+        // Spawn a new thread to perform block production for the validator.
         let producer_thread = {
             let spec = spec.clone();
             let duties_map = duties_map.clone();
@@ -152,6 +157,7 @@ fn main() {
         threads.push((duties_manager_thread, producer_thread));
     }
 
+    // Naively wait for all the threads to complete.
     for tuple in threads {
         let (manager, producer) = tuple;
         let _ = producer.join();