diff --git a/src/state/transition/ffg.rs b/src/state/transition/ffg.rs
new file mode 100644
index 000000000..7b63b47d3
--- /dev/null
+++ b/src/state/transition/ffg.rs
@@ -0,0 +1,192 @@
+use std::collections::HashMap;
+
+use super::crystallized_state::CrystallizedState;
+use super::partial_crosslink_record::PartialCrosslinkRecord;
+use super::aggregate_vote::AggregateVote;
+use super::config::Config;
+use super::utils::types::Bitfield;
+use super::utils::bls::PublicKey;
+use super::crosslinks::{ 
+    get_crosslink_shards, 
+    get_crosslink_aggvote_msg,
+    get_crosslink_notaries };
+
+pub fn update_ffg_and_crosslink_progress(
+    cry_state: &CrystallizedState,
+    partial_crosslinks: &Vec<PartialCrosslinkRecord>,
+    ffg_voter_bitfield: &Bitfield,
+    aggregate_votes: &Vec<AggregateVote>,
+    config: &Config)
+    -> (Vec<PartialCrosslinkRecord>, Bitfield, usize)
+{
+    let mut vote_key_bitfield_map: HashMap<Vec<u8>, Bitfield> =
+        HashMap::new();
+    for pc in partial_crosslinks {
+       vote_key_bitfield_map.insert(pc.vote_key(), pc.voter_bitfield.clone());
+    }
+    let mut global_bitfield = ffg_voter_bitfield.clone();
+    let mut total_voters: usize = 0;
+    let crosslink_shards: Vec<u16> = get_crosslink_shards(
+        &cry_state, &config);
+
+    for av in aggregate_votes {
+        let attestation = get_crosslink_aggvote_msg(
+            &av,
+            &cry_state);
+        let validator_indicies = get_crosslink_notaries(
+            &cry_state,
+            &av.shard_id,
+            &crosslink_shards);
+        let mut crosslink_bitfield = match vote_key_bitfield_map.get(&av.vote_key()) {
+            None => Bitfield::new(),
+            Some(existing_bitfield) => existing_bitfield.clone()
+        };
+        let mut public_keys: Vec<&PublicKey> = vec![];
+        for (i, vi) in validator_indicies.iter().enumerate() {
+            if av.notary_bitfield.get_bit(&i) {
+                public_keys.push(&cry_state.active_validators[i].pubkey);
+                if global_bitfield.get_bit(&vi) == false {
+                    global_bitfield.set_bit(&vi, &true);
+                    crosslink_bitfield.set_bit(&i, &true);
+                    total_voters += 1;
+                }
+            }
+        }
+        // TODO: add bls verfification here, it is completely bypassed
+        assert_eq!(attestation, attestation);   // fixes warning
+
+        vote_key_bitfield_map.insert(av.vote_key(), crosslink_bitfield);
+    }
+    
+    let mut new_partial_crosslinks: Vec<PartialCrosslinkRecord> = vec![];
+    for (vote_key, bitfield) in vote_key_bitfield_map {
+        new_partial_crosslinks.push(PartialCrosslinkRecord::new_from_vote_key(
+                &vote_key,
+                bitfield));
+    }
+
+    (new_partial_crosslinks, global_bitfield, total_voters)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use super::super::shuffling::get_shuffling;
+    use super::super::super::validator_record::ValidatorRecord;
+    use super::super::super::super::utils::types::{ Sha256Digest, Bitfield };
+    use super::super::super::super::utils::bls::AggregateSignature;
+    
+    #[test]
+    fn test_update_ffg_and_crosslink_progress_scenario_1() {
+        let mut cry_state = CrystallizedState::zero();
+        let mut config = Config::standard();
+
+        // Create some shard_ids and associated hashes
+        let shard_ids: Vec<u16> = (0..10).collect();
+        let shard_hashes: Vec<Sha256Digest> = shard_ids.iter()  
+            .map(|_| Sha256Digest::random()).collect();
+       
+        // Define which shards with have partial crosslinks and which will
+        // have aggregate votes. Note: there should be some overlap here.
+        let shards_with_partial_crosslinks: Vec<u16> = shard_ids[0..5].to_vec();
+        let shards_with_aggregate_votes: Vec<u16> = shard_ids[4..10].to_vec();
+
+        // Update the config to neatly fit the shards we created. 
+        config.shard_count = shard_ids.len() as u16;
+        config.notaries_per_crosslink = 10;
+       
+        // Create just enough validators to notarise each shard
+        let validator_count: usize = 
+            (config.shard_count * config.notaries_per_crosslink) as usize;
+       
+        // Load active validators into the cry_state
+        (0..validator_count).for_each(
+            |_| cry_state.active_validators.push(
+                ValidatorRecord::zero_with_thread_rand_pub_key()));
+        
+        // Set a shuffling for the validators 
+        let s = get_shuffling(
+            &Sha256Digest::zero(),
+            &cry_state.num_active_validators(),
+            &config);
+        cry_state.current_shuffling = s.clone();
+
+        // Create the required partial crosslink records 
+        let partial_crosslinks: Vec<PartialCrosslinkRecord> = 
+            shards_with_partial_crosslinks
+            .iter()  
+            .map(|i| {
+                let mut bitfield = Bitfield::new();
+                // Only the first 7 validators should sign the partial xlinks
+                for i in 0..7 {
+                    bitfield.set_bit(&i, &true);
+                }
+                PartialCrosslinkRecord {
+                    shard_id: *i,
+                    shard_block_hash: shard_hashes[*i as usize],
+                    voter_bitfield: bitfield
+                }
+            }).collect();
+        
+        let mut total_aggregate_sig_votes = 0;
+        let mut aggregate_sig_bitfield = Bitfield::new();
+
+        // Create the required aggregate votes
+        let aggregate_votes: Vec<AggregateVote> = shards_with_aggregate_votes
+            .iter()  
+            .map(|i| {
+                let validator_indicies = get_crosslink_notaries(
+                    &cry_state,
+                    i,
+                    &shard_ids);
+                let mut bitfield = Bitfield::new();
+                // Only the last 2 validators should sign the aggregate votes
+                for i in 8..10 {
+                    bitfield.set_bit(&i, &true);
+                    total_aggregate_sig_votes += 1;
+                    aggregate_sig_bitfield.set_bit(&validator_indicies[i], &true)
+                }
+                AggregateVote {
+                    shard_id: *i,
+                    shard_block_hash: shard_hashes[*i as usize],
+                    notary_bitfield: bitfield,
+                    aggregate_sig: AggregateSignature::new()
+                }
+            }).collect();
+        assert_eq!(aggregate_votes.len(), shards_with_aggregate_votes.len(), 
+                   "test setup failed.");
+
+        let (new_partial_crosslinks, global_bitfield, vote_count) = 
+            update_ffg_and_crosslink_progress(
+            &cry_state,
+            &partial_crosslinks,
+            &Bitfield::new(),
+            &aggregate_votes,
+            &config);
+
+        assert_eq!(total_aggregate_sig_votes, vote_count, 
+                   "The total votes returned did not \
+                   match our running tally.");
+        
+        assert_eq!(total_aggregate_sig_votes, 
+                   global_bitfield.num_true_bits() as usize,
+                   "The FFG field did not have as many true \
+                   bits as expected.");
+
+        assert!(aggregate_sig_bitfield == global_bitfield);
+
+        for pc in new_partial_crosslinks {
+            let id = pc.shard_id;
+            let mut vote_count = 0;
+            if shards_with_partial_crosslinks.contains(&id) {
+                vote_count += 7;
+            }
+            if shards_with_aggregate_votes.contains(&id) {
+                vote_count += 2;
+            }
+            assert_eq!(pc.voter_bitfield.num_true_bits(), vote_count,
+            "shard_id {} failed.", id);
+            assert_eq!(pc.shard_block_hash, shard_hashes[id as usize]);
+        }
+    }
+}
diff --git a/src/state/transition/mod.rs b/src/state/transition/mod.rs
index 2393dc72e..84ae6682b 100644
--- a/src/state/transition/mod.rs
+++ b/src/state/transition/mod.rs
@@ -11,6 +11,7 @@ use super::validator_record;
 
 pub mod crosslinks;
 pub mod deposits;
+pub mod ffg;
 pub mod shuffling;
 pub mod validators;
 pub mod attestors;