diff --git a/beacon_node/beacon_chain/test_harness/examples/chain.yaml b/beacon_node/beacon_chain/test_harness/examples/chain.yaml
index 919753afa..036871aeb 100644
--- a/beacon_node/beacon_chain/test_harness/examples/chain.yaml
+++ b/beacon_node/beacon_chain/test_harness/examples/chain.yaml
@@ -19,6 +19,17 @@ test_cases:
         - slot: 5
           amount: 32
           merkle_index: 2
+      proposer_slashings:
+        - slot: 8 # At slot 8, we trigger a proposal slashing occurring
+          proposer_index: 42 # We penalize the validator at position 42
+          proposal_1_shard: 0
+          proposal_1_slot: 15
+          proposal_1_root: !!binary |
+            LkmqmqoodLKAslkjdkajsdljasdkajlksjdasldjasdd
+          proposal_2_shard: 0
+          proposal_2_slot: 15
+          proposal_2_root: !!binary |
+            DIFFERENTKAslkjdkajsdljasdkajlksjdasldjasdd
     results:
       num_validators: 1000
   - config:
diff --git a/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs b/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs
index b60454b57..43b60d506 100644
--- a/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs
+++ b/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs
@@ -10,6 +10,7 @@ use fork_choice::BitwiseLMDGhost;
 use log::debug;
 use rayon::prelude::*;
 use slot_clock::TestingSlotClock;
+use ssz::TreeHash;
 use std::collections::HashSet;
 use std::fs::File;
 use std::io::prelude::*;
@@ -242,7 +243,7 @@ impl BeaconChainHarness {
         debug!("Free attestations processed.");
     }
 
-    pub fn process_deposit(&mut self, deposit: Deposit, keypair: Option<Keypair>) {
+    pub fn add_deposit(&mut self, deposit: Deposit, keypair: Option<Keypair>) {
         self.beacon_chain.receive_deposit_for_inclusion(deposit);
 
         // If a keypair is present, add a new `ValidatorHarness` to the rig.
@@ -253,6 +254,36 @@ impl BeaconChainHarness {
         }
     }
 
+    pub fn add_proposer_slashing(&mut self, mut proposer_slashing: ProposerSlashing) {
+        let validator = &self.validators[proposer_slashing.proposer_index as usize];
+
+        // This following code is a little awkward, but managing the data_1 and data_1 was getting
+        // rather confusing. I think this is better
+        let proposals = vec![
+            &proposer_slashing.proposal_data_1,
+            &proposer_slashing.proposal_data_2,
+        ];
+        let signatures: Vec<Signature> = proposals
+            .iter()
+            .map(|proposal_data| {
+                let message = proposal_data.hash_tree_root();
+                let epoch = proposal_data.slot.epoch(self.spec.epoch_length);
+                let domain = self
+                    .beacon_chain
+                    .state
+                    .read()
+                    .fork
+                    .get_domain(epoch, self.spec.domain_proposal);
+                Signature::new(&message[..], domain, &validator.keypair.sk)
+            })
+            .collect();
+        proposer_slashing.proposal_signature_1 = signatures[0].clone();
+        proposer_slashing.proposal_signature_2 = signatures[1].clone();
+
+        self.beacon_chain
+            .receive_proposer_slashing_for_inclusion(proposer_slashing);
+    }
+
     pub fn run_fork_choice(&mut self) {
         self.beacon_chain.fork_choice().unwrap()
     }
diff --git a/beacon_node/beacon_chain/test_harness/src/bin.rs b/beacon_node/beacon_chain/test_harness/src/bin.rs
index f747be60a..e905e9342 100644
--- a/beacon_node/beacon_chain/test_harness/src/bin.rs
+++ b/beacon_node/beacon_chain/test_harness/src/bin.rs
@@ -85,12 +85,25 @@ impl Manifest {
         info!("Starting simulation across {} slots...", slots);
 
         for slot_height in 0..slots {
-            // Include deposits
+            // Feed deposits to the BeaconChain.
             if let Some(ref deposits) = self.config.deposits {
                 for (slot, deposit, keypair) in deposits {
                     if *slot == slot_height {
                         info!("Including deposit at slot height {}.", slot_height);
-                        harness.process_deposit(deposit.clone(), Some(keypair.clone()));
+                        harness.add_deposit(deposit.clone(), Some(keypair.clone()));
+                    }
+                }
+            }
+
+            // Feed proposer slashings to the BeaconChain.
+            if let Some(ref slashings) = self.config.proposer_slashings {
+                for (slot, slashing) in slashings {
+                    if *slot == slot_height {
+                        info!(
+                            "Including proposer slashing at slot height {}.",
+                            slot_height
+                        );
+                        harness.add_proposer_slashing(slashing.clone());
                     }
                 }
             }
@@ -163,6 +176,7 @@ impl Manifest {
 }
 
 pub type DepositTuple = (u64, Deposit, Keypair);
+pub type ProposerSlashingTuple = (u64, ProposerSlashing);
 
 struct ExecutionResult {
     pub chain: Vec<CheckPoint>,
@@ -190,6 +204,7 @@ struct Config {
     pub num_slots: u64,
     pub skip_slots: Option<Vec<u64>>,
     pub deposits: Option<Vec<DepositTuple>>,
+    pub proposer_slashings: Option<Vec<ProposerSlashingTuple>>,
 }
 
 impl Config {
@@ -200,12 +215,52 @@ impl Config {
             epoch_length: as_u64(&yaml, "epoch_length"),
             num_slots: as_u64(&yaml, "num_slots").expect("Must specify `config.num_slots`"),
             skip_slots: as_vec_u64(yaml, "skip_slots"),
-            deposits: process_deposits(&yaml),
+            deposits: parse_deposits(&yaml),
+            proposer_slashings: parse_proposer_slashings(&yaml),
         }
     }
 }
 
-fn process_deposits(yaml: &Yaml) -> Option<Vec<DepositTuple>> {
+fn parse_proposer_slashings(yaml: &Yaml) -> Option<Vec<ProposerSlashingTuple>> {
+    let mut slashings = vec![];
+
+    for slashing in yaml["proposer_slashings"].as_vec()? {
+        let slot = as_u64(slashing, "slot").expect("Incomplete slashing");
+
+        let slashing = ProposerSlashing {
+            proposer_index: as_u64(slashing, "proposer_index")
+                .expect("Incomplete slashing (proposer_index)"),
+            proposal_data_1: ProposalSignedData {
+                slot: Slot::from(
+                    as_u64(slashing, "proposal_1_slot")
+                        .expect("Incomplete slashing (proposal_1_slot)."),
+                ),
+                shard: as_u64(slashing, "proposal_1_shard")
+                    .expect("Incomplete slashing (proposal_1_shard)."),
+                block_root: as_hash256(slashing, "proposal_1_root")
+                    .expect("Incomplete slashing (proposal_1_root)."),
+            },
+            proposal_signature_1: Signature::empty_signature(), // Will be replaced with real signature at runtime.
+            proposal_data_2: ProposalSignedData {
+                slot: Slot::from(
+                    as_u64(slashing, "proposal_2_slot")
+                        .expect("Incomplete slashing (proposal_2_slot)."),
+                ),
+                shard: as_u64(slashing, "proposal_2_shard")
+                    .expect("Incomplete slashing (proposal_2_shard)."),
+                block_root: as_hash256(slashing, "proposal_2_root")
+                    .expect("Incomplete slashing (proposal_2_root)."),
+            },
+            proposal_signature_2: Signature::empty_signature(), // Will be replaced with real signature at runtime.
+        };
+
+        slashings.push((slot, slashing));
+    }
+
+    Some(slashings)
+}
+
+fn parse_deposits(yaml: &Yaml) -> Option<Vec<DepositTuple>> {
     let mut deposits = vec![];
 
     for deposit in yaml["deposits"].as_vec()? {
@@ -241,6 +296,12 @@ fn as_u64(yaml: &Yaml, key: &str) -> Option<u64> {
     yaml[key].as_i64().and_then(|n| Some(n as u64))
 }
 
+fn as_hash256(yaml: &Yaml, key: &str) -> Option<Hash256> {
+    yaml[key]
+        .as_str()
+        .and_then(|s| Some(Hash256::from(s.as_bytes())))
+}
+
 fn as_vec_u64(yaml: &Yaml, key: &str) -> Option<Vec<u64>> {
     yaml[key].clone().into_vec().and_then(|vec| {
         Some(