diff --git a/eth2/beacon/state_machines/forks/serenity/block_processing.py b/eth2/beacon/state_machines/forks/serenity/block_processing.py
new file mode 100644
index 0000000000..e4960db7cb
--- /dev/null
+++ b/eth2/beacon/state_machines/forks/serenity/block_processing.py
@@ -0,0 +1,39 @@
+from eth_utils.toolz import (
+    first,
+)
+
+from eth2._utils.tuple import update_tuple_item
+
+from eth2.beacon.types.states import BeaconState
+from eth2.beacon.types.blocks import BaseBeaconBlock
+from eth2.beacon.types.eth1_data_vote import Eth1DataVote
+
+from eth2.beacon.state_machines.configs import BeaconConfig
+
+
+def process_eth1_data(state: BeaconState,
+                      block: BaseBeaconBlock,
+                      config: BeaconConfig) -> BeaconState:
+    try:
+        vote_index, original_vote = first(
+            (index, eth1_data_vote)
+            for index, eth1_data_vote in enumerate(state.eth1_data_votes)
+            if block.eth1_data == eth1_data_vote.eth1_data
+        )
+    except StopIteration:
+        new_vote = Eth1DataVote(
+            eth1_data=block.eth1_data,
+            vote_count=1,
+        )
+        state = state.copy(
+            eth1_data_votes=state.eth1_data_votes + (new_vote,)
+        )
+    else:
+        updated_vote = original_vote.copy(
+            vote_count=original_vote.vote_count + 1
+        )
+        state = state.copy(
+            eth1_data_votes=update_tuple_item(state.eth1_data_votes, vote_index, updated_vote)
+        )
+
+    return state
diff --git a/tests/eth2/beacon/state_machines/forks/test_serenity_block_processing.py b/tests/eth2/beacon/state_machines/forks/test_serenity_block_processing.py
new file mode 100644
index 0000000000..8c680f5bae
--- /dev/null
+++ b/tests/eth2/beacon/state_machines/forks/test_serenity_block_processing.py
@@ -0,0 +1,44 @@
+import pytest
+
+from eth2.beacon.types.eth1_data_vote import Eth1DataVote
+from eth2.beacon.types.states import BeaconState
+from eth2.beacon.types.blocks import BeaconBlock
+
+from eth2.beacon.state_machines.forks.serenity.block_processing import (
+    process_eth1_data,
+)
+
+HASH1 = b"\x11" * 32
+HASH2 = b"\x22" * 32
+
+
+@pytest.mark.parametrize(("original_votes", "block_data", "expected_votes"), (
+    ((), HASH1, ((HASH1, 1),)),
+    (((HASH1, 5),), HASH1, ((HASH1, 6),)),
+    (((HASH2, 5),), HASH1, ((HASH2, 5), (HASH1, 1))),
+    (((HASH1, 10), (HASH2, 2)), HASH2, ((HASH1, 10), (HASH2, 3))),
+))
+def test_process_eth1_data(original_votes,
+                           block_data,
+                           expected_votes,
+                           sample_beacon_state_params,
+                           sample_beacon_block_params,
+                           config):
+    eth1_data_votes = tuple(
+        Eth1DataVote(data, vote_count)
+        for data, vote_count in original_votes
+    )
+    state = BeaconState(**sample_beacon_state_params).copy(
+        eth1_data_votes=eth1_data_votes,
+    )
+
+    block = BeaconBlock(**sample_beacon_block_params).copy(
+        eth1_data=block_data,
+    )
+
+    updated_state = process_eth1_data(state, block, config)
+    updated_votes = tuple(
+        (vote.eth1_data, vote.vote_count)
+        for vote in updated_state.eth1_data_votes
+    )
+    assert updated_votes == expected_votes