diff --git a/lighthouse/main.rs b/lighthouse/main.rs
index 257ef1b6b5..1631cc4e74 100644
--- a/lighthouse/main.rs
+++ b/lighthouse/main.rs
@@ -6,11 +6,12 @@ extern crate clap;
 extern crate network_libp2p;
 extern crate futures;
 
+#[macro_use]
+pub mod utils;
 pub mod db;
 pub mod client;
 pub mod state;
 pub mod sync;
-pub mod utils;
 pub mod config;
 
 use std::path::PathBuf;
diff --git a/lighthouse/state/helpers.rs b/lighthouse/state/helpers.rs
new file mode 100644
index 0000000000..388fedafbf
--- /dev/null
+++ b/lighthouse/state/helpers.rs
@@ -0,0 +1,71 @@
+/*
+ * Collection of helper functions used in the state transition modules
+ */
+use super::active_state::ActiveState;
+use super::block::Block;
+use super::chain_config::ChainConfig;
+use super::utils::errors::ParameterError;
+use super::utils::types::Hash256;
+
+/*
+   pub fn get_signed_parent_hashes(
+   active_state: &ActiveState,
+   block: &Block,
+   attestation: &AttestationRecord,
+   chain_config: &ChainConfig)
+   -> Vec<Hash256> {
+   }
+   */
+
+pub fn get_block_hash(
+    active_state_recent_block_hashes: &Vec<Hash256>,
+    current_block_slot: &u64,
+    slot: &u64,
+    cycle_length: &u64, // convert from standard u8
+) -> Result<Hash256, ParameterError> {
+    // active_state must have at 2*cycle_length hashes
+    assert_error!(
+        active_state_recent_block_hashes.len() as u64 == cycle_length * 2,
+        ParameterError::InvalidInput(String::from(
+            "active state has incorrect number of block hashes"
+        ))
+    );
+
+    let state_start_slot = (*current_block_slot)
+        .checked_sub(cycle_length * 2)
+        .unwrap_or(0);
+
+    assert_error!(
+        (state_start_slot <= *slot) && (*slot < *current_block_slot),
+        ParameterError::InvalidInput(String::from("incorrect slot number"))
+    );
+
+    let index = 2 * cycle_length + (*slot) - *current_block_slot; // should always be positive
+    Ok(active_state_recent_block_hashes[index as usize])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_get_block_hash() {
+        let block_slot: u64 = 10;
+        let slot: u64 = 3;
+        let cycle_length: u64 = 8;
+
+        let mut block_hashes: Vec<Hash256> = Vec::new();
+        for _i in 0..2 * cycle_length {
+            block_hashes.push(Hash256::random());
+        }
+
+        let result = get_block_hash(&block_hashes, &block_slot, &slot, &cycle_length).unwrap();
+
+        assert_eq!(
+            result,
+            block_hashes[(2 * cycle_length + slot - block_slot) as usize]
+        );
+
+        println!("{:?}", result);
+    }
+}
diff --git a/lighthouse/state/mod.rs b/lighthouse/state/mod.rs
index 8f8f748d87..fbb789490c 100644
--- a/lighthouse/state/mod.rs
+++ b/lighthouse/state/mod.rs
@@ -17,3 +17,5 @@ pub mod crosslink_record;
 pub mod shard_and_committee;
 pub mod transition;
 pub mod validator_record;
+pub mod validation;
+pub mod helpers;
diff --git a/lighthouse/state/transition/attestation_parent_hashes.rs b/lighthouse/state/transition/attestation_parent_hashes.rs
index 35866159fe..2ba4712d55 100644
--- a/lighthouse/state/transition/attestation_parent_hashes.rs
+++ b/lighthouse/state/transition/attestation_parent_hashes.rs
@@ -1,5 +1,5 @@
 use super::Hash256;
-use super::TransitionError;
+use super::ParameterError;
 
 /// This function is used to select the hashes used in
 /// the signing of an AttestationRecord.
@@ -18,22 +18,22 @@ pub fn attestation_parent_hashes(
     attestation_slot: u64,
     current_hashes: &[Hash256],
     oblique_hashes: &[Hash256])
-    -> Result<Vec<Hash256>, TransitionError>
+    -> Result<Vec<Hash256>, ParameterError>
 {
     // This cast places a limit on cycle_length. If you change it, check math
     // for overflow.
     let cycle_length: u64 = u64::from(cycle_length);
 
     if current_hashes.len() as u64 != (cycle_length * 2) {
-        return Err(TransitionError::InvalidInput(String::from(
+        return Err(ParameterError::InvalidInput(String::from(
                     "current_hashes.len() must equal cycle_length * 2")));
     }
     if attestation_slot >= block_slot {
-        return Err(TransitionError::InvalidInput(String::from(
+        return Err(ParameterError::InvalidInput(String::from(
                     "attestation_slot must be less than block_slot")));
     }
     if oblique_hashes.len() as u64 > cycle_length {
-        return Err(TransitionError::InvalidInput(String::from(
+        return Err(ParameterError::InvalidInput(String::from(
                     "oblique_hashes.len() must be <= cycle_length * 2")));
     }
 
@@ -44,7 +44,7 @@ pub fn attestation_parent_hashes(
     let attestation_distance = block_slot - attestation_slot;
 
     if attestation_distance > cycle_length {
-        return Err(TransitionError::InvalidInput(String::from(
+        return Err(ParameterError::InvalidInput(String::from(
                     "attestation_slot must be withing one cycle of block_slot")));
     }
 
@@ -63,7 +63,7 @@ pub fn attestation_parent_hashes(
      */
     let end = start.checked_add(cycle_length)
         .and_then(|x| x.checked_sub(oblique_hashes.len() as u64))
-        .ok_or(TransitionError::IntWrapping)?;
+        .ok_or(ParameterError::IntWrapping)?;
 
 
     let mut hashes = Vec::new();
diff --git a/lighthouse/state/transition/mod.rs b/lighthouse/state/transition/mod.rs
index 2d4592f303..de80e4961d 100644
--- a/lighthouse/state/transition/mod.rs
+++ b/lighthouse/state/transition/mod.rs
@@ -1,6 +1,7 @@
 use super::block;
 use super::Logger;
 use super::utils::types::Hash256;
+use super::utils::errors::ParameterError;
 use super::db;
 
 mod attestation_parent_hashes;
@@ -10,12 +11,6 @@ mod validate_block;
 pub use self::attestation_parent_hashes::attestation_parent_hashes;
 pub use self::shuffling::shuffle;
 
-#[derive(Debug)]
-pub enum TransitionError {
-    IntWrapping,
-    OutOfBounds,
-    InvalidInput(String),
-}
 
 
 
diff --git a/lighthouse/state/validation/attestation_validation.rs b/lighthouse/state/validation/attestation_validation.rs
new file mode 100644
index 0000000000..4704320638
--- /dev/null
+++ b/lighthouse/state/validation/attestation_validation.rs
@@ -0,0 +1,81 @@
+use super::CrystallizedState;
+use super::ActiveState;
+use super::AttestationRecord;
+use super::Block;
+use super::ChainConfig;
+
+use ::utils::errors::AttestationValidationError;
+
+// implementation of validate_attestation in the v2.1 python reference implementation
+// see: https://github.com/ethereum/beacon_chain/blob/a79ab2c6f03cbdabf2b6d9d435c26e2b216e09a5/beacon_chain/state/state_transition.py#L61
+pub fn validate_attestation(
+    crystallized_state: &CrystallizedState,
+    active_state: &ActiveState,
+    attestation: &AttestationRecord,
+    block: &Block,
+    chain_config: &ChainConfig)
+    -> Result<bool, AttestationValidationError> {
+
+        if !(attestation.slot < block.slot_number) {
+            return Err(AttestationValidationError::SlotTooHigh);
+        }
+
+        if !(attestation.slot > (block.slot_number - chain_config.cycle_length as u64)) {
+            return Err(AttestationValidationError::SlotTooLow(format!("Attestation slot number too low\n\tFound: {:?}, Needed greater than: {:?}", attestation.slot, block.slot_number - chain_config.cycle_length as u64)));
+        }
+
+        Ok(true)
+    }
+
+
+#[cfg(test)]
+mod tests {
+
+    use super::*;
+    // test helper functions
+
+    fn generate_standard_state() -> (
+        CrystallizedState,
+        ActiveState,
+        AttestationRecord,
+        Block,
+        ChainConfig) {
+
+        let crystallized_state = CrystallizedState::zero();
+        let active_state = ActiveState::zero();
+        let attestation_record = AttestationRecord::zero();
+        let block = Block::zero();
+        let chain_config = ChainConfig::standard();
+
+        return (crystallized_state, active_state, attestation_record, block, chain_config);
+    }
+
+    #[test]
+    fn test_attestation_validation_slot_high() {
+        // generate standard state
+        let (crystallized_state, active_state, mut attestation_record, mut block, chain_config) = generate_standard_state();
+        // set slot too high
+        attestation_record.slot = 30;
+        block.slot_number = 10;
+
+        let result = validate_attestation(&crystallized_state, &active_state, &attestation_record, &block, &chain_config);
+        assert_eq!(result, Err(AttestationValidationError::SlotTooHigh));
+    }
+
+    #[test]
+    fn test_attestation_validation_slot_low() {
+        // generate standard state
+        let (crystallized_state, active_state, mut attestation_record, mut block, chain_config) = generate_standard_state();
+        // set slot too high
+        attestation_record.slot = 2;
+        block.slot_number = 10;
+
+        let result = validate_attestation(
+            &crystallized_state,
+            &active_state,
+            &attestation_record,
+            &block,
+            &chain_config);
+        //assert_eq!(result, Err(AttestationValidationError::SlotTooLow));
+    }
+}
diff --git a/lighthouse/state/validation/mod.rs b/lighthouse/state/validation/mod.rs
new file mode 100644
index 0000000000..c11b652612
--- /dev/null
+++ b/lighthouse/state/validation/mod.rs
@@ -0,0 +1,7 @@
+use super::crystallized_state::CrystallizedState;
+use super::active_state::ActiveState;
+use super::attestation_record::AttestationRecord;
+use super::block::Block;
+use super::chain_config::ChainConfig;
+
+mod attestation_validation;
diff --git a/lighthouse/utils/errors.rs b/lighthouse/utils/errors.rs
new file mode 100644
index 0000000000..2a25b29b8e
--- /dev/null
+++ b/lighthouse/utils/errors.rs
@@ -0,0 +1,17 @@
+// Collection of custom errors
+
+#[derive(Debug,PartialEq)]
+pub enum AttestationValidationError {
+    SlotTooHigh,
+    SlotTooLow(String),
+    IncorrectBitField,
+    NonZeroTrailingBits,
+    AggregateSignatureFail
+}
+
+#[derive(Debug,PartialEq)]
+pub enum ParameterError {
+    IntWrapping,
+    OutOfBounds,
+    InvalidInput(String),
+}
diff --git a/lighthouse/utils/macros.rs b/lighthouse/utils/macros.rs
new file mode 100644
index 0000000000..e6e3be01ec
--- /dev/null
+++ b/lighthouse/utils/macros.rs
@@ -0,0 +1,10 @@
+#[macro_export]
+macro_rules! assert_error {
+    ($exp: expr, $err: expr) => {
+        if ( !$exp ) {
+            return Err($err);
+        }
+    }
+}
+
+
diff --git a/lighthouse/utils/mod.rs b/lighthouse/utils/mod.rs
index cfb302d4b4..4afe15c454 100644
--- a/lighthouse/utils/mod.rs
+++ b/lighthouse/utils/mod.rs
@@ -3,8 +3,13 @@ extern crate blake2_rfc as blake2;
 extern crate crypto_mac;
 extern crate boolean_bitfield;
 
+#[macro_use]
+pub mod macros;
 pub mod hash;
 pub mod types;
 pub mod bls;
 pub mod test_helpers;
 pub mod logging;
+pub mod errors;
+
+