diff --git a/eth2/types/src/attestation.rs b/eth2/types/src/attestation.rs
index bef35bc78..c7ce07ab6 100644
--- a/eth2/types/src/attestation.rs
+++ b/eth2/types/src/attestation.rs
@@ -1,5 +1,5 @@
 use super::bls::AggregateSignature;
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::{AttestationData, Bitfield};
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -49,6 +49,17 @@ impl Attestation {
     }
 }
 
+impl TreeHash for Attestation {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.data.hash_tree_root());
+        result.append(&mut self.aggregation_bitfield.hash_tree_root());
+        result.append(&mut self.custody_bitfield.hash_tree_root());
+        result.append(&mut self.aggregate_signature.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Attestation {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -76,4 +87,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Attestation::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/attestation_data.rs b/eth2/types/src/attestation_data.rs
index c1e895d6c..1744f0dd0 100644
--- a/eth2/types/src/attestation_data.rs
+++ b/eth2/types/src/attestation_data.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::Hash256;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -85,6 +85,21 @@ impl Decodable for AttestationData {
     }
 }
 
+impl TreeHash for AttestationData {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.slot.hash_tree_root());
+        result.append(&mut self.shard.hash_tree_root());
+        result.append(&mut self.beacon_block_root.hash_tree_root());
+        result.append(&mut self.epoch_boundary_root.hash_tree_root());
+        result.append(&mut self.shard_block_root.hash_tree_root());
+        result.append(&mut self.latest_crosslink_root.hash_tree_root());
+        result.append(&mut self.justified_slot.hash_tree_root());
+        result.append(&mut self.justified_block_root.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for AttestationData {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -116,4 +131,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = AttestationData::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/attestation_data_and_custody_bit.rs b/eth2/types/src/attestation_data_and_custody_bit.rs
index 66584b0d9..6265c0d06 100644
--- a/eth2/types/src/attestation_data_and_custody_bit.rs
+++ b/eth2/types/src/attestation_data_and_custody_bit.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{Decodable, DecodeError, Encodable, hash, TreeHash, SszStream};
 use rand::RngCore;
 use crate::test_utils::TestRandom;
 use super::AttestationData;
@@ -30,6 +30,16 @@ impl Decodable for AttestationDataAndCustodyBit {
     }
 }
 
+impl TreeHash for AttestationDataAndCustodyBit {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let result: Vec<u8> = vec![];
+        result.append(&mut self.data.hash_tree_root());
+        // TODO: add bool ssz
+        // result.append(custody_bit.hash_tree_root());
+        ssz::hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for AttestationDataAndCustodyBit {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -57,4 +67,16 @@ mod test {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = AttestationDataAndCustodyBit::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/beacon_block.rs b/eth2/types/src/beacon_block.rs
index 4dff199f3..50945df8b 100644
--- a/eth2/types/src/beacon_block.rs
+++ b/eth2/types/src/beacon_block.rs
@@ -1,4 +1,4 @@
-use super::ssz::{ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, ssz_encode, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::{BeaconBlockBody, Eth1Data, Hash256};
 use crate::test_utils::TestRandom;
 use bls::Signature;
@@ -61,6 +61,20 @@ impl Decodable for BeaconBlock {
     }
 }
 
+impl TreeHash for BeaconBlock {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.slot.hash_tree_root());
+        result.append(&mut self.parent_root.hash_tree_root());
+        result.append(&mut self.state_root.hash_tree_root());
+        result.append(&mut self.randao_reveal.hash_tree_root());
+        result.append(&mut self.eth1_data.hash_tree_root());
+        result.append(&mut self.signature.hash_tree_root());
+        result.append(&mut self.body.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for BeaconBlock {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -91,4 +105,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = BeaconBlock::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/beacon_block_body.rs b/eth2/types/src/beacon_block_body.rs
index 67fa34d91..d530e74dc 100644
--- a/eth2/types/src/beacon_block_body.rs
+++ b/eth2/types/src/beacon_block_body.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::{Attestation, CasperSlashing, Deposit, Exit, ProposerSlashing};
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -61,6 +61,21 @@ impl Decodable for BeaconBlockBody {
     }
 }
 
+impl TreeHash for BeaconBlockBody {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.proposer_slashings.hash_tree_root());
+        result.append(&mut self.casper_slashings.hash_tree_root());
+        result.append(&mut self.attestations.hash_tree_root());
+        result.append(&mut self.custody_reseeds.hash_tree_root());
+        result.append(&mut self.custody_challenges.hash_tree_root());
+        result.append(&mut self.custody_responses.hash_tree_root());
+        result.append(&mut self.deposits.hash_tree_root());
+        result.append(&mut self.exits.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for BeaconBlockBody {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -92,4 +107,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = BeaconBlockBody::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/beacon_state.rs b/eth2/types/src/beacon_state.rs
index 34afeaa83..0de06fa60 100644
--- a/eth2/types/src/beacon_state.rs
+++ b/eth2/types/src/beacon_state.rs
@@ -3,12 +3,12 @@ use super::eth1_data::Eth1Data;
 use super::eth1_data_vote::Eth1DataVote;
 use super::fork::Fork;
 use super::pending_attestation::PendingAttestation;
+use super::ssz::{hash, ssz_encode, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::validator::Validator;
 use super::Hash256;
 use crate::test_utils::TestRandom;
 use hashing::canonical_hash;
 use rand::RngCore;
-use ssz::{ssz_encode, Decodable, DecodeError, Encodable, SszStream};
 
 // Custody will not be added to the specs until Phase 1 (Sharding Phase) so dummy class used.
 type CustodyChallenge = usize;
@@ -166,6 +166,41 @@ impl Decodable for BeaconState {
     }
 }
 
+impl TreeHash for BeaconState {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.slot.hash_tree_root());
+        result.append(&mut self.genesis_time.hash_tree_root());
+        result.append(&mut self.fork_data.hash_tree_root());
+        result.append(&mut self.validator_registry.hash_tree_root());
+        result.append(&mut self.validator_balances.hash_tree_root());
+        result.append(&mut self.validator_registry_update_slot.hash_tree_root());
+        result.append(&mut self.validator_registry_exit_count.hash_tree_root());
+        result.append(&mut self.validator_registry_delta_chain_tip.hash_tree_root());
+        result.append(&mut self.latest_randao_mixes.hash_tree_root());
+        result.append(&mut self.latest_vdf_outputs.hash_tree_root());
+        result.append(&mut self.previous_epoch_start_shard.hash_tree_root());
+        result.append(&mut self.current_epoch_start_shard.hash_tree_root());
+        result.append(&mut self.previous_epoch_calculation_slot.hash_tree_root());
+        result.append(&mut self.current_epoch_calculation_slot.hash_tree_root());
+        result.append(&mut self.previous_epoch_randao_mix.hash_tree_root());
+        result.append(&mut self.current_epoch_randao_mix.hash_tree_root());
+        result.append(&mut self.custody_challenges.hash_tree_root());
+        result.append(&mut self.previous_justified_slot.hash_tree_root());
+        result.append(&mut self.justified_slot.hash_tree_root());
+        result.append(&mut self.justification_bitfield.hash_tree_root());
+        result.append(&mut self.finalized_slot.hash_tree_root());
+        result.append(&mut self.latest_crosslinks.hash_tree_root());
+        result.append(&mut self.latest_block_roots.hash_tree_root());
+        result.append(&mut self.latest_penalized_exit_balances.hash_tree_root());
+        result.append(&mut self.latest_attestations.hash_tree_root());
+        result.append(&mut self.batched_block_roots.hash_tree_root());
+        result.append(&mut self.latest_eth1_data.hash_tree_root());
+        result.append(&mut self.eth1_data_votes.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for BeaconState {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -217,4 +252,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = BeaconState::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/casper_slashing.rs b/eth2/types/src/casper_slashing.rs
index 08dbd9ff3..62bad76dd 100644
--- a/eth2/types/src/casper_slashing.rs
+++ b/eth2/types/src/casper_slashing.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::SlashableVoteData;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -31,6 +31,15 @@ impl Decodable for CasperSlashing {
     }
 }
 
+impl TreeHash for CasperSlashing {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.slashable_vote_data_1.hash_tree_root());
+        result.append(&mut self.slashable_vote_data_2.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for CasperSlashing {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -56,4 +65,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = CasperSlashing::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/crosslink.rs b/eth2/types/src/crosslink.rs
index 69f94662a..dfb02993d 100644
--- a/eth2/types/src/crosslink.rs
+++ b/eth2/types/src/crosslink.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::Hash256;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -41,6 +41,15 @@ impl Decodable for Crosslink {
     }
 }
 
+impl TreeHash for Crosslink {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.slot.hash_tree_root());
+        result.append(&mut self.shard_block_root.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Crosslink {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -66,4 +75,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Crosslink::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/deposit.rs b/eth2/types/src/deposit.rs
index 9d84bc278..d2f112ec8 100644
--- a/eth2/types/src/deposit.rs
+++ b/eth2/types/src/deposit.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::{DepositData, Hash256};
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -35,6 +35,16 @@ impl Decodable for Deposit {
     }
 }
 
+impl TreeHash for Deposit {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.merkle_branch.hash_tree_root());
+        result.append(&mut self.merkle_tree_index.hash_tree_root());
+        result.append(&mut self.deposit_data.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Deposit {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -61,4 +71,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Deposit::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/deposit_data.rs b/eth2/types/src/deposit_data.rs
index b85a95708..21ca6cd51 100644
--- a/eth2/types/src/deposit_data.rs
+++ b/eth2/types/src/deposit_data.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::DepositInput;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -35,6 +35,16 @@ impl Decodable for DepositData {
     }
 }
 
+impl TreeHash for DepositData {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.amount.hash_tree_root());
+        result.append(&mut self.timestamp.hash_tree_root());
+        result.append(&mut self.deposit_input.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for DepositData {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -61,4 +71,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = DepositData::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/deposit_input.rs b/eth2/types/src/deposit_input.rs
index 4f2d71096..5377926d6 100644
--- a/eth2/types/src/deposit_input.rs
+++ b/eth2/types/src/deposit_input.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::Hash256;
 use crate::test_utils::TestRandom;
 use bls::{PublicKey, Signature};
@@ -36,6 +36,16 @@ impl Decodable for DepositInput {
     }
 }
 
+impl TreeHash for DepositInput {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.pubkey.hash_tree_root());
+        result.append(&mut self.withdrawal_credentials.hash_tree_root());
+        result.append(&mut self.proof_of_possession.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for DepositInput {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -62,4 +72,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = DepositInput::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/eth1_data.rs b/eth2/types/src/eth1_data.rs
index a20559e18..6d9e67a4a 100644
--- a/eth2/types/src/eth1_data.rs
+++ b/eth2/types/src/eth1_data.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::Hash256;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -32,6 +32,15 @@ impl Decodable for Eth1Data {
     }
 }
 
+impl TreeHash for Eth1Data {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.deposit_root.hash_tree_root());
+        result.append(&mut self.block_hash.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Eth1Data {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -57,4 +66,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Eth1Data::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/eth1_data_vote.rs b/eth2/types/src/eth1_data_vote.rs
index c4d9d01af..09a9a7954 100644
--- a/eth2/types/src/eth1_data_vote.rs
+++ b/eth2/types/src/eth1_data_vote.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::Eth1Data;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -32,6 +32,15 @@ impl Decodable for Eth1DataVote {
     }
 }
 
+impl TreeHash for Eth1DataVote {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.eth1_data.hash_tree_root());
+        result.append(&mut self.vote_count.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Eth1DataVote {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -57,4 +66,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Eth1DataVote::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/exit.rs b/eth2/types/src/exit.rs
index eeac11ce7..f70d26e41 100644
--- a/eth2/types/src/exit.rs
+++ b/eth2/types/src/exit.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use crate::test_utils::TestRandom;
 use bls::Signature;
 use rand::RngCore;
@@ -35,6 +35,16 @@ impl Decodable for Exit {
     }
 }
 
+impl TreeHash for Exit {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.slot.hash_tree_root());
+        result.append(&mut self.validator_index.hash_tree_root());
+        result.append(&mut self.signature.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Exit {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -61,4 +71,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Exit::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/fork.rs b/eth2/types/src/fork.rs
index b70dafccc..7915299a1 100644
--- a/eth2/types/src/fork.rs
+++ b/eth2/types/src/fork.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use crate::test_utils::TestRandom;
 use rand::RngCore;
 
@@ -34,6 +34,16 @@ impl Decodable for Fork {
     }
 }
 
+impl TreeHash for Fork {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.pre_fork_version.hash_tree_root());
+        result.append(&mut self.post_fork_version.hash_tree_root());
+        result.append(&mut self.fork_slot.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Fork {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -60,4 +70,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Fork::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/pending_attestation.rs b/eth2/types/src/pending_attestation.rs
index ad3dbb782..89ac7b07c 100644
--- a/eth2/types/src/pending_attestation.rs
+++ b/eth2/types/src/pending_attestation.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::{AttestationData, Bitfield};
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -39,6 +39,17 @@ impl Decodable for PendingAttestation {
     }
 }
 
+impl TreeHash for PendingAttestation {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.data.hash_tree_root());
+        result.append(&mut self.aggregation_bitfield.hash_tree_root());
+        result.append(&mut self.custody_bitfield.hash_tree_root());
+        result.append(&mut self.custody_bitfield.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for PendingAttestation {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -66,4 +77,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = PendingAttestation::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/proposal_signed_data.rs b/eth2/types/src/proposal_signed_data.rs
index e38a9cadb..41f0cda81 100644
--- a/eth2/types/src/proposal_signed_data.rs
+++ b/eth2/types/src/proposal_signed_data.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::Hash256;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
@@ -35,6 +35,16 @@ impl Decodable for ProposalSignedData {
     }
 }
 
+impl TreeHash for ProposalSignedData {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.slot.hash_tree_root());
+        result.append(&mut self.shard.hash_tree_root());
+        result.append(&mut self.block_root.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for ProposalSignedData {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -61,4 +71,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = ProposalSignedData::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/proposer_slashing.rs b/eth2/types/src/proposer_slashing.rs
index 3754c3b32..8d9a843e2 100644
--- a/eth2/types/src/proposer_slashing.rs
+++ b/eth2/types/src/proposer_slashing.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::ProposalSignedData;
 use crate::test_utils::TestRandom;
 use bls::Signature;
@@ -44,6 +44,18 @@ impl Decodable for ProposerSlashing {
     }
 }
 
+impl TreeHash for ProposerSlashing {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.proposer_index.hash_tree_root());
+        result.append(&mut self.proposal_data_1.hash_tree_root());
+        result.append(&mut self.proposal_signature_1.hash_tree_root());
+        result.append(&mut self.proposal_data_2.hash_tree_root());
+        result.append(&mut self.proposal_signature_2.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for ProposerSlashing {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -72,4 +84,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = ProposerSlashing::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/shard_committee.rs b/eth2/types/src/shard_committee.rs
index d920f7db3..3e7202b2a 100644
--- a/eth2/types/src/shard_committee.rs
+++ b/eth2/types/src/shard_committee.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use crate::test_utils::TestRandom;
 use rand::RngCore;
 
@@ -24,6 +24,15 @@ impl Decodable for ShardCommittee {
     }
 }
 
+impl TreeHash for ShardCommittee {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.shard.hash_tree_root());
+        result.append(&mut self.committee.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for ShardCommittee {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -49,4 +58,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = ShardCommittee::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/shard_reassignment_record.rs b/eth2/types/src/shard_reassignment_record.rs
index 9bc014689..8f48692fc 100644
--- a/eth2/types/src/shard_reassignment_record.rs
+++ b/eth2/types/src/shard_reassignment_record.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use crate::test_utils::TestRandom;
 use rand::RngCore;
 
@@ -34,6 +34,16 @@ impl Decodable for ShardReassignmentRecord {
     }
 }
 
+impl TreeHash for ShardReassignmentRecord {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.validator_index.hash_tree_root());
+        result.append(&mut self.shard.hash_tree_root());
+        result.append(&mut self.slot.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for ShardReassignmentRecord {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -60,4 +70,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = ShardReassignmentRecord::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/slashable_vote_data.rs b/eth2/types/src/slashable_vote_data.rs
index e6fa36bc1..3f088034f 100644
--- a/eth2/types/src/slashable_vote_data.rs
+++ b/eth2/types/src/slashable_vote_data.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::AttestationData;
 use crate::test_utils::TestRandom;
 use bls::AggregateSignature;
@@ -40,6 +40,17 @@ impl Decodable for SlashableVoteData {
     }
 }
 
+impl TreeHash for SlashableVoteData {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.custody_bit_0_indices.hash_tree_root());
+        result.append(&mut self.custody_bit_1_indices.hash_tree_root());
+        result.append(&mut self.data.hash_tree_root());
+        result.append(&mut self.aggregate_signature.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for SlashableVoteData {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -67,4 +78,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = SlashableVoteData::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/special_record.rs b/eth2/types/src/special_record.rs
index 0a0a6978a..21e9c88f6 100644
--- a/eth2/types/src/special_record.rs
+++ b/eth2/types/src/special_record.rs
@@ -1,4 +1,4 @@
-use super::ssz::{Decodable, DecodeError, Encodable, SszStream};
+use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
 /// The value of the "type" field of SpecialRecord.
 ///
@@ -71,6 +71,15 @@ impl Decodable for SpecialRecord {
     }
 }
 
+impl TreeHash for SpecialRecord {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.kind.hash_tree_root());
+        result.append(&mut self.data.as_slice().hash_tree_root());
+        hash(&result)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/eth2/types/src/validator.rs b/eth2/types/src/validator.rs
index 8408e7423..256be68df 100644
--- a/eth2/types/src/validator.rs
+++ b/eth2/types/src/validator.rs
@@ -2,7 +2,7 @@ use super::bls::PublicKey;
 use super::Hash256;
 use crate::test_utils::TestRandom;
 use rand::RngCore;
-use ssz::{Decodable, DecodeError, Encodable, SszStream};
+use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
 const STATUS_FLAG_INITIATED_EXIT: u8 = 1;
 const STATUS_FLAG_WITHDRAWABLE: u8 = 2;
@@ -142,6 +142,24 @@ impl Decodable for Validator {
     }
 }
 
+impl TreeHash for Validator {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.pubkey.hash_tree_root());
+        result.append(&mut self.withdrawal_credentials.hash_tree_root());
+        result.append(&mut self.proposer_slots.hash_tree_root());
+        result.append(&mut self.activation_slot.hash_tree_root());
+        result.append(&mut self.exit_slot.hash_tree_root());
+        result.append(&mut self.withdrawal_slot.hash_tree_root());
+        result.append(&mut self.penalized_slot.hash_tree_root());
+        result.append(&mut self.exit_count.hash_tree_root());
+        result.append(&mut (status_flag_to_byte(self.status_flags) as u64).hash_tree_root());
+        result.append(&mut self.latest_custody_reseed_slot.hash_tree_root());
+        result.append(&mut self.penultimate_custody_reseed_slot.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for Validator {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -198,4 +216,16 @@ mod tests {
             }
         }
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = Validator::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/types/src/validator_registry_delta_block.rs b/eth2/types/src/validator_registry_delta_block.rs
index 57aa469df..c8bf41c94 100644
--- a/eth2/types/src/validator_registry_delta_block.rs
+++ b/eth2/types/src/validator_registry_delta_block.rs
@@ -2,7 +2,7 @@ use super::Hash256;
 use crate::test_utils::TestRandom;
 use bls::PublicKey;
 use rand::RngCore;
-use ssz::{Decodable, DecodeError, Encodable, SszStream};
+use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
 // The information gathered from the PoW chain validator registration function.
 #[derive(Debug, Clone, PartialEq)]
@@ -58,6 +58,18 @@ impl Decodable for ValidatorRegistryDeltaBlock {
     }
 }
 
+impl TreeHash for ValidatorRegistryDeltaBlock {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut result: Vec<u8> = vec![];
+        result.append(&mut self.latest_registry_delta_root.hash_tree_root());
+        result.append(&mut self.validator_index.hash_tree_root());
+        result.append(&mut self.pubkey.hash_tree_root());
+        result.append(&mut self.slot.hash_tree_root());
+        result.append(&mut self.flag.hash_tree_root());
+        hash(&result)
+    }
+}
+
 impl<T: RngCore> TestRandom<T> for ValidatorRegistryDeltaBlock {
     fn random_for_test(rng: &mut T) -> Self {
         Self {
@@ -86,4 +98,16 @@ mod tests {
 
         assert_eq!(original, decoded);
     }
+
+    #[test]
+    pub fn test_hash_tree_root() {
+        let mut rng = XorShiftRng::from_seed([42; 16]);
+        let original = ValidatorRegistryDeltaBlock::random_for_test(&mut rng);
+
+        let result = original.hash_tree_root();
+
+        assert_eq!(result.len(), 32);
+        // TODO: Add further tests
+        // https://github.com/sigp/lighthouse/issues/170
+    }
 }
diff --git a/eth2/utils/bls/src/aggregate_signature.rs b/eth2/utils/bls/src/aggregate_signature.rs
index 6012f78c1..6bccf128e 100644
--- a/eth2/utils/bls/src/aggregate_signature.rs
+++ b/eth2/utils/bls/src/aggregate_signature.rs
@@ -1,4 +1,4 @@
-use super::ssz::{decode_ssz_list, Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{decode_ssz_list, hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::{AggregatePublicKey, Signature};
 use bls_aggregates::AggregateSignature as RawAggregateSignature;
 
@@ -44,6 +44,12 @@ impl Decodable for AggregateSignature {
     }
 }
 
+impl TreeHash for AggregateSignature {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        hash(&self.0.as_bytes())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::super::ssz::ssz_encode;
diff --git a/eth2/utils/bls/src/public_key.rs b/eth2/utils/bls/src/public_key.rs
index 4a53893f0..d0635e6f5 100644
--- a/eth2/utils/bls/src/public_key.rs
+++ b/eth2/utils/bls/src/public_key.rs
@@ -1,7 +1,9 @@
 use super::SecretKey;
 use bls_aggregates::PublicKey as RawPublicKey;
 use hex::encode as hex_encode;
-use ssz::{decode_ssz_list, ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{
+    decode_ssz_list, hash, ssz_encode, Decodable, DecodeError, Encodable, SszStream, TreeHash,
+};
 use std::default;
 use std::hash::{Hash, Hasher};
 
@@ -53,6 +55,12 @@ impl Decodable for PublicKey {
     }
 }
 
+impl TreeHash for PublicKey {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        hash(&self.0.as_bytes())
+    }
+}
+
 impl PartialEq for PublicKey {
     fn eq(&self, other: &PublicKey) -> bool {
         ssz_encode(self) == ssz_encode(other)
diff --git a/eth2/utils/bls/src/secret_key.rs b/eth2/utils/bls/src/secret_key.rs
index e86e8dec0..3327d94d6 100644
--- a/eth2/utils/bls/src/secret_key.rs
+++ b/eth2/utils/bls/src/secret_key.rs
@@ -1,5 +1,5 @@
 use bls_aggregates::{DecodeError as BlsDecodeError, SecretKey as RawSecretKey};
-use ssz::{decode_ssz_list, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{decode_ssz_list, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
 /// A single BLS signature.
 ///
@@ -40,6 +40,12 @@ impl Decodable for SecretKey {
     }
 }
 
+impl TreeHash for SecretKey {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        self.0.as_bytes().clone()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::super::ssz::ssz_encode;
diff --git a/eth2/utils/bls/src/signature.rs b/eth2/utils/bls/src/signature.rs
index 7f9e61718..9e4945bb7 100644
--- a/eth2/utils/bls/src/signature.rs
+++ b/eth2/utils/bls/src/signature.rs
@@ -1,4 +1,4 @@
-use super::ssz::{decode_ssz_list, Decodable, DecodeError, Encodable, SszStream};
+use super::ssz::{decode_ssz_list, hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use super::{PublicKey, SecretKey};
 use bls_aggregates::Signature as RawSignature;
 
@@ -57,6 +57,12 @@ impl Decodable for Signature {
     }
 }
 
+impl TreeHash for Signature {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        hash(&self.0.as_bytes())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::super::ssz::ssz_encode;
diff --git a/eth2/utils/boolean-bitfield/src/lib.rs b/eth2/utils/boolean-bitfield/src/lib.rs
index 98518d70c..33c461361 100644
--- a/eth2/utils/boolean-bitfield/src/lib.rs
+++ b/eth2/utils/boolean-bitfield/src/lib.rs
@@ -149,6 +149,12 @@ impl ssz::Decodable for BooleanBitfield {
     }
 }
 
+impl ssz::TreeHash for BooleanBitfield {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        self.to_bytes().hash_tree_root()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/eth2/utils/ssz/src/impl_encode.rs b/eth2/utils/ssz/src/impl_encode.rs
index 63de18058..8714cf75f 100644
--- a/eth2/utils/ssz/src/impl_encode.rs
+++ b/eth2/utils/ssz/src/impl_encode.rs
@@ -79,6 +79,14 @@ mod tests {
         assert_eq!(ssz.drain(), vec![0; 32]);
     }
 
+    #[test]
+    fn test_ssz_encode_address() {
+        let h = Address::zero();
+        let mut ssz = SszStream::new();
+        ssz.append(&h);
+        assert_eq!(ssz.drain(), vec![0; 20]);
+    }
+
     #[test]
     fn test_ssz_encode_u8() {
         let x: u8 = 0;
diff --git a/eth2/utils/ssz/src/impl_tree_hash.rs b/eth2/utils/ssz/src/impl_tree_hash.rs
index 229b5549a..9463283cb 100644
--- a/eth2/utils/ssz/src/impl_tree_hash.rs
+++ b/eth2/utils/ssz/src/impl_tree_hash.rs
@@ -1,51 +1,54 @@
-extern crate hashing;
-
-use self::hashing::canonical_hash;
 use super::ethereum_types::{Address, H256};
-use super::{merkle_hash, ssz_encode, TreeHash};
-use std::cmp::Ord;
-use std::collections::HashMap;
-use std::hash::Hash;
+use super::{hash, merkle_hash, ssz_encode, TreeHash};
 
 impl TreeHash for u8 {
-    fn tree_hash(&self) -> Vec<u8> {
+    fn hash_tree_root(&self) -> Vec<u8> {
         ssz_encode(self)
     }
 }
 
 impl TreeHash for u16 {
-    fn tree_hash(&self) -> Vec<u8> {
+    fn hash_tree_root(&self) -> Vec<u8> {
         ssz_encode(self)
     }
 }
 
 impl TreeHash for u32 {
-    fn tree_hash(&self) -> Vec<u8> {
+    fn hash_tree_root(&self) -> Vec<u8> {
         ssz_encode(self)
     }
 }
 
 impl TreeHash for u64 {
-    fn tree_hash(&self) -> Vec<u8> {
+    fn hash_tree_root(&self) -> Vec<u8> {
+        ssz_encode(self)
+    }
+}
+
+impl TreeHash for usize {
+    fn hash_tree_root(&self) -> Vec<u8> {
         ssz_encode(self)
     }
 }
 
 impl TreeHash for Address {
-    fn tree_hash(&self) -> Vec<u8> {
+    fn hash_tree_root(&self) -> Vec<u8> {
         ssz_encode(self)
     }
 }
 
 impl TreeHash for H256 {
-    fn tree_hash(&self) -> Vec<u8> {
+    fn hash_tree_root(&self) -> Vec<u8> {
         ssz_encode(self)
     }
 }
 
 impl TreeHash for [u8] {
-    fn tree_hash(&self) -> Vec<u8> {
-        hash(&self)
+    fn hash_tree_root(&self) -> Vec<u8> {
+        if self.len() > 32 {
+            return hash(&self);
+        }
+        self.to_vec()
     }
 }
 
@@ -53,71 +56,23 @@ impl<T> TreeHash for Vec<T>
 where
     T: TreeHash,
 {
-    /// Returns the merkle_hash of a list of tree_hash values created
+    /// Returns the merkle_hash of a list of hash_tree_root values created
     /// from the given list.
     /// Note: A byte vector, Vec<u8>, must be converted to a slice (as_slice())
     ///       to be handled properly (i.e. hashed) as byte array.
-    fn tree_hash(&self) -> Vec<u8> {
-        let mut tree_hashes = self.iter().map(|x| x.tree_hash()).collect();
+    fn hash_tree_root(&self) -> Vec<u8> {
+        let mut tree_hashes = self.iter().map(|x| x.hash_tree_root()).collect();
         merkle_hash(&mut tree_hashes)
     }
 }
 
-impl<K, V> TreeHash for HashMap<K, V>
-where
-    K: Eq,
-    K: Hash,
-    K: Ord,
-    V: TreeHash,
-{
-    /// Appends the tree_hash for each value of 'self, sorted by key,
-    /// into a byte array and returns the hash of said byte array
-    fn tree_hash(&self) -> Vec<u8> {
-        let mut items: Vec<_> = self.iter().collect();
-        items.sort_by(|a, b| a.0.cmp(b.0));
-        let mut result = Vec::new();
-        for item in items {
-            result.append(&mut item.1.tree_hash());
-        }
-
-        hash(&result)
-    }
-}
-
-fn hash(data: &[u8]) -> Vec<u8> {
-    canonical_hash(data)
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
     fn test_impl_tree_hash_vec() {
-        let result = vec![1u32, 2, 3, 4, 5, 6, 7].tree_hash();
+        let result = vec![1u32, 2, 3, 4, 5, 6, 7].hash_tree_root();
         assert_eq!(result.len(), 32);
     }
-
-    #[test]
-    fn test_impl_tree_hash_hashmap() {
-        let mut map = HashMap::new();
-        map.insert("c", 3);
-        map.insert("b", 2);
-        map.insert("g", 7);
-        map.insert("d", 6);
-        map.insert("e", 4);
-        map.insert("a", 1u32);
-        map.insert("f", 5);
-        let result = map.tree_hash();
-
-        // TODO: create tests that tie-out to an offical result
-        assert_eq!(
-            result,
-            [
-                130, 215, 165, 255, 224, 6, 144, 225, 14, 139, 67, 238, 205, 240, 20, 173, 53, 0,
-                105, 62, 49, 174, 244, 160, 114, 92, 232, 11, 102, 200, 112, 24
-            ]
-        );
-    }
-
 }
diff --git a/eth2/utils/ssz/src/lib.rs b/eth2/utils/ssz/src/lib.rs
index bea15c054..206040c2d 100644
--- a/eth2/utils/ssz/src/lib.rs
+++ b/eth2/utils/ssz/src/lib.rs
@@ -20,7 +20,7 @@ mod impl_tree_hash;
 
 pub use crate::decode::{decode_ssz, decode_ssz_list, Decodable, DecodeError};
 pub use crate::encode::{Encodable, SszStream};
-pub use crate::tree_hash::{merkle_hash, TreeHash};
+pub use crate::tree_hash::{hash, merkle_hash, TreeHash};
 
 pub const LENGTH_BYTES: usize = 4;
 pub const MAX_LIST_SIZE: usize = 1 << (4 * 8);
diff --git a/eth2/utils/ssz/src/tree_hash.rs b/eth2/utils/ssz/src/tree_hash.rs
index 912be110a..5f62c1c7b 100644
--- a/eth2/utils/ssz/src/tree_hash.rs
+++ b/eth2/utils/ssz/src/tree_hash.rs
@@ -1,48 +1,41 @@
+use hashing::canonical_hash;
+
 const SSZ_CHUNK_SIZE: usize = 128;
 const HASHSIZE: usize = 32;
 
 pub trait TreeHash {
-    fn tree_hash(&self) -> Vec<u8>;
+    fn hash_tree_root(&self) -> Vec<u8>;
 }
 
 /// Returns a 32 byte hash of 'list' - a vector of byte vectors.
 /// Note that this will consume 'list'.
 pub fn merkle_hash(list: &mut Vec<Vec<u8>>) -> Vec<u8> {
     // flatten list
-    let (chunk_size, mut data) = list_to_blob(list);
+    let (chunk_size, mut chunkz) = list_to_blob(list);
 
     // get data_len as bytes. It will hashed will the merkle root
-    let dlen = list.len() as u64;
-    let data_len_bytes = &mut dlen.tree_hash();
-    data_len_bytes.resize(32, 0);
+    let datalen = list.len().to_le_bytes();
 
-    // merklize
-    let mut mhash = hash_level(&mut data, chunk_size);
-    while mhash.len() > HASHSIZE {
-        mhash = hash_level(&mut mhash, HASHSIZE);
-    }
+    // Tree-hash
+    while chunkz.len() > HASHSIZE {
+        let mut new_chunkz: Vec<u8> = Vec::new();
 
-    mhash.append(data_len_bytes);
-    mhash.as_slice().tree_hash()
-}
-
-/// Takes a flat vector of bytes. It then hashes 'chunk_size * 2' slices into
-/// a byte vector of hashes, divisible by HASHSIZE
-fn hash_level(data: &mut Vec<u8>, chunk_size: usize) -> Vec<u8> {
-    let mut result: Vec<u8> = Vec::new();
-    for two_chunks in data.chunks(chunk_size * 2) {
-        if two_chunks.len() == chunk_size && data.len() > chunk_size {
-            // if there is only one chunk here, hash it with a zero-byte
-            // SSZ_CHUNK_SIZE vector
-            let mut c = two_chunks.to_vec();
-            c.append(&mut vec![0; SSZ_CHUNK_SIZE]);
-            result.append(&mut c.as_slice().tree_hash());
-        } else {
-            result.append(&mut two_chunks.tree_hash());
+        for two_chunks in chunkz.chunks(chunk_size * 2) {
+            if two_chunks.len() == chunk_size {
+                // Odd number of chunks
+                let mut c = two_chunks.to_vec();
+                c.append(&mut vec![0; SSZ_CHUNK_SIZE]);
+                new_chunkz.append(&mut hash(&c));
+            } else {
+                // Hash two chuncks together
+                new_chunkz.append(&mut hash(two_chunks));
+            }
         }
+        chunkz = new_chunkz;
     }
 
-    result
+    chunkz.append(&mut datalen.to_vec());
+    hash(&chunkz)
 }
 
 fn list_to_blob(list: &mut Vec<Vec<u8>>) -> (usize, Vec<u8>) {
@@ -67,10 +60,13 @@ fn list_to_blob(list: &mut Vec<Vec<u8>>) -> (usize, Vec<u8>) {
             data.append(item);
         }
     }
-
     (chunk_size, data)
 }
 
+pub fn hash(data: &[u8]) -> Vec<u8> {
+    canonical_hash(data)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;