diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 838178ea4..d8d3d6a76 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -346,8 +346,8 @@ class AttestationData(Container):
     # LMD GHOST vote
     beacon_block_root: Hash
     # FFG vote
-    source_checkpoint: Checkpoint
-    target_checkpoint: Checkpoint
+    source: Checkpoint
+    target: Checkpoint
     # Crosslink vote
     crosslink: Crosslink
 ```
@@ -719,10 +719,9 @@ def get_epoch_start_shard(state: BeaconState, epoch: Epoch) -> Shard:
 
 ```python
 def get_attestation_data_slot(state: BeaconState, data: AttestationData) -> Slot:
-    target_epoch = data.target_checkpoint.epoch
-    committee_count = get_epoch_committee_count(state, target_epoch)
-    offset = (data.crosslink.shard + SHARD_COUNT - get_epoch_start_shard(state, target_epoch)) % SHARD_COUNT
-    return Slot(get_epoch_start_slot(target_epoch) + offset // (committee_count // SLOTS_PER_EPOCH))
+    committee_count = get_epoch_committee_count(state, data.target.epoch)
+    offset = (data.crosslink.shard + SHARD_COUNT - get_epoch_start_shard(state, data.target.epoch)) % SHARD_COUNT
+    return Slot(get_epoch_start_slot(data.target.epoch) + offset // (committee_count // SLOTS_PER_EPOCH))
 ```
 
 ### `get_block_root_at_slot`
@@ -886,7 +885,7 @@ def get_attesting_indices(state: BeaconState,
     """
     Return the sorted attesting indices corresponding to ``data`` and ``bitfield``.
     """
-    committee = get_crosslink_committee(state, data.target_checkpoint.epoch, data.crosslink.shard)
+    committee = get_crosslink_committee(state, data.target.epoch, data.crosslink.shard)
     assert verify_bitfield(bitfield, len(committee))
     return sorted([index for i, index in enumerate(committee) if get_bitfield_bit(bitfield, i) == 0b1])
 ```
@@ -1006,7 +1005,7 @@ def validate_indexed_attestation(state: BeaconState, indexed_attestation: Indexe
             hash_tree_root(AttestationDataAndCustodyBit(data=indexed_attestation.data, custody_bit=0b1)),
         ],
         signature=indexed_attestation.signature,
-        domain=get_domain(state, DOMAIN_ATTESTATION, indexed_attestation.data.target_checkpoint.epoch),
+        domain=get_domain(state, DOMAIN_ATTESTATION, indexed_attestation.data.target.epoch),
     )
 ```
 
@@ -1019,12 +1018,9 @@ def is_slashable_attestation_data(data_1: AttestationData, data_2: AttestationDa
     """
     return (
         # Double vote
-        (data_1 != data_2 and data_1.target_checkpoint.epoch == data_2.target_checkpoint.epoch) or
+        (data_1 != data_2 and data_1.target.epoch == data_2.target.epoch) or
         # Surround vote
-        (
-            data_1.source_checkpoint.epoch < data_2.source_checkpoint.epoch and
-            data_2.target_checkpoint.epoch < data_1.target_checkpoint.epoch
-        )
+        (data_1.source.epoch < data_2.source.epoch and data_2.target.epoch < data_1.target.epoch)
     )
 ```
 
@@ -1282,7 +1278,7 @@ def get_matching_source_attestations(state: BeaconState, epoch: Epoch) -> List[P
 def get_matching_target_attestations(state: BeaconState, epoch: Epoch) -> List[PendingAttestation]:
     return [
         a for a in get_matching_source_attestations(state, epoch)
-        if a.data.target_checkpoint.root == get_block_root(state, epoch)
+        if a.data.target.root == get_block_root(state, epoch)
     ]
 ```
 
@@ -1344,13 +1340,13 @@ def process_justification_and_finalization(state: BeaconState) -> None:
         state, get_matching_target_attestations(state, previous_epoch)
     )
     if previous_epoch_matching_target_balance * 3 >= get_total_active_balance(state) * 2:
-        state.current_justified_checkpoint = Checkpoint(epoch=previous_epoch, root=get_block_root(state, previous_epoch))
+        state.current_justified_checkpoint = Checkpoint(previous_epoch, get_block_root(state, previous_epoch))
         state.justification_bitfield |= (1 << 1)
     current_epoch_matching_target_balance = get_attesting_balance(
         state, get_matching_target_attestations(state, current_epoch)
     )
     if current_epoch_matching_target_balance * 3 >= get_total_active_balance(state) * 2:
-        state.current_justified_checkpoint = Checkpoint(epoch=current_epoch, root=get_block_root(state, current_epoch))
+        state.current_justified_checkpoint = Checkpoint(current_epoch, get_block_root(state, current_epoch))
         state.justification_bitfield |= (1 << 0)
 
     # Process finalizations
@@ -1692,10 +1688,8 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
     Process ``Attestation`` operation.
     """
     data = attestation.data
-    target_epoch = data.target_checkpoint.epoch
-
     assert data.crosslink.shard < SHARD_COUNT
-    assert target_epoch in (get_previous_epoch(state), get_current_epoch(state))
+    assert data.target.epoch in (get_previous_epoch(state), get_current_epoch(state))
 
     attestation_slot = get_attestation_data_slot(state, data)
     assert attestation_slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= attestation_slot + SLOTS_PER_EPOCH
@@ -1707,7 +1701,7 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
         proposer_index=get_beacon_proposer_index(state),
     )
 
-    if target_epoch == get_current_epoch(state):
+    if data.target.epoch == get_current_epoch(state):
         ffg_source = state.current_justified_checkpoint
         parent_crosslink = state.current_crosslinks[data.crosslink.shard]
         state.current_epoch_attestations.append(pending_attestation)
@@ -1717,9 +1711,9 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
         state.previous_epoch_attestations.append(pending_attestation)
 
     # Check FFG source, crosslink data, and signature
-    assert ffg_source == data.source_checkpoint
+    assert ffg_source == data.source
     assert data.crosslink.start_epoch == parent_crosslink.end_epoch
-    assert data.crosslink.end_epoch == min(target_epoch, parent_crosslink.end_epoch + MAX_EPOCHS_PER_CROSSLINK)
+    assert data.crosslink.end_epoch == min(data.target.epoch, parent_crosslink.end_epoch + MAX_EPOCHS_PER_CROSSLINK)
     assert data.crosslink.parent_root == hash_tree_root(parent_crosslink)
     assert data.crosslink.data_root == ZERO_HASH  # [to be removed in phase 1]
     validate_indexed_attestation(state, convert_to_indexed(state, attestation))
diff --git a/test_libs/pyspec/eth2spec/test/helpers/attestations.py b/test_libs/pyspec/eth2spec/test/helpers/attestations.py
index d2ce6e29b..d717bdc0d 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/attestations.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/attestations.py
@@ -37,8 +37,8 @@ def build_attestation_data(spec, state, slot, shard):
 
     return spec.AttestationData(
         beacon_block_root=block_root,
-        source_checkpoint=spec.Checkpoint(epoch=source_epoch, root=source_root),
-        target_checkpoint=spec.Checkpoint(epoch=spec.slot_to_epoch(slot), root=epoch_boundary_root),
+        source=spec.Checkpoint(epoch=source_epoch, root=source_root),
+        target=spec.Checkpoint(epoch=spec.slot_to_epoch(slot), root=epoch_boundary_root),
         crosslink=spec.Crosslink(
             shard=shard,
             start_epoch=parent_crosslink.end_epoch,
@@ -62,7 +62,7 @@ def get_valid_attestation(spec, state, slot=None, signed=False):
 
     crosslink_committee = spec.get_crosslink_committee(
         state,
-        attestation_data.target_checkpoint.epoch,
+        attestation_data.target.epoch,
         attestation_data.crosslink.shard,
     )
 
@@ -124,7 +124,7 @@ def get_attestation_signature(spec, state, attestation_data, privkey, custody_bi
         domain=spec.get_domain(
             state=state,
             domain_type=spec.DOMAIN_ATTESTATION,
-            message_epoch=attestation_data.target_checkpoint.epoch,
+            message_epoch=attestation_data.target.epoch,
         )
     )
 
@@ -132,7 +132,7 @@ def get_attestation_signature(spec, state, attestation_data, privkey, custody_bi
 def fill_aggregate_attestation(spec, state, attestation):
     crosslink_committee = spec.get_crosslink_committee(
         state,
-        attestation.data.target_checkpoint.epoch,
+        attestation.data.target.epoch,
         attestation.data.crosslink.shard,
     )
     for i in range(len(crosslink_committee)):
diff --git a/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py b/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py
index e339421e8..9c68b7bbe 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/attester_slashings.py
@@ -7,7 +7,7 @@ def get_valid_attester_slashing(spec, state, signed_1=False, signed_2=False):
     attestation_1 = get_valid_attestation(spec, state, signed=signed_1)
 
     attestation_2 = deepcopy(attestation_1)
-    attestation_2.data.target_checkpoint.root = b'\x01' * 32
+    attestation_2.data.target.root = b'\x01' * 32
 
     if signed_2:
         sign_attestation(spec, state, attestation_2)
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
index 9a718b071..d6cb615f8 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attestation.py
@@ -38,7 +38,7 @@ def run_attestation_processing(spec, state, attestation, valid=True):
     spec.process_attestation(state, attestation)
 
     # Make sure the attestation has been processed
-    if attestation.data.target_checkpoint.epoch == spec.get_current_epoch(state):
+    if attestation.data.target.epoch == spec.get_current_epoch(state):
         assert len(state.current_epoch_attestations) == current_epoch_count + 1
     else:
         assert len(state.previous_epoch_attestations) == previous_epoch_count + 1
@@ -125,10 +125,10 @@ def test_old_source_epoch(spec, state):
     attestation = get_valid_attestation(spec, state, slot=(spec.SLOTS_PER_EPOCH * 3) + 1)
 
     # test logic sanity check: make sure the attestation is pointing to oldest known source epoch
-    assert attestation.data.source_checkpoint.epoch == state.previous_justified_checkpoint.epoch
+    assert attestation.data.source.epoch == state.previous_justified_checkpoint.epoch
 
     # Now go beyond that, it will be invalid
-    attestation.data.source_checkpoint.epoch -= 1
+    attestation.data.source.epoch -= 1
 
     sign_attestation(spec, state, attestation)
 
@@ -154,7 +154,7 @@ def test_new_source_epoch(spec, state):
     attestation = get_valid_attestation(spec, state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.source_checkpoint.epoch += 1
+    attestation.data.source.epoch += 1
 
     sign_attestation(spec, state, attestation)
 
@@ -167,7 +167,7 @@ def test_source_root_is_target_root(spec, state):
     attestation = get_valid_attestation(spec, state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.source_checkpoint.root = attestation.data.target_checkpoint.root
+    attestation.data.source.root = attestation.data.target.root
 
     sign_attestation(spec, state, attestation)
 
@@ -188,10 +188,10 @@ def test_invalid_current_source_root(spec, state):
 
     # Test logic sanity checks:
     assert state.current_justified_checkpoint.root != state.previous_justified_checkpoint.root
-    assert attestation.data.source_checkpoint.root == state.previous_justified_checkpoint.root
+    assert attestation.data.source.root == state.previous_justified_checkpoint.root
 
     # Make attestation source root invalid: should be previous justified, not current one
-    attestation.data.source_checkpoint.root = state.current_justified_checkpoint.root
+    attestation.data.source.root = state.current_justified_checkpoint.root
 
     sign_attestation(spec, state, attestation)
 
@@ -204,7 +204,7 @@ def test_bad_source_root(spec, state):
     attestation = get_valid_attestation(spec, state)
     state.slot += spec.MIN_ATTESTATION_INCLUSION_DELAY
 
-    attestation.data.source_checkpoint.root = b'\x42' * 32
+    attestation.data.source.root = b'\x42' * 32
 
     sign_attestation(spec, state, attestation)
 
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
index 71915f1d0..e2b50ea0b 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/block_processing/test_process_attester_slashing.py
@@ -74,8 +74,8 @@ def test_success_surround(spec, state):
     attestation_2 = attester_slashing.attestation_2
 
     # set attestion1 to surround attestation 2
-    attestation_1.data.source_checkpoint.epoch = attestation_2.data.source_checkpoint.epoch - 1
-    attestation_1.data.target_checkpoint.epoch = attestation_2.data.target_checkpoint.epoch + 1
+    attestation_1.data.source.epoch = attestation_2.data.source.epoch - 1
+    attestation_1.data.target.epoch = attestation_2.data.target.epoch + 1
 
     sign_indexed_attestation(spec, state, attester_slashing.attestation_1)
 
@@ -122,7 +122,7 @@ def test_same_data(spec, state):
 def test_no_double_or_surround(spec, state):
     attester_slashing = get_valid_attester_slashing(spec, state, signed_1=False, signed_2=True)
 
-    attester_slashing.attestation_1.data.target_checkpoint.epoch += 1
+    attester_slashing.attestation_1.data.target.epoch += 1
     sign_indexed_attestation(spec, state, attester_slashing.attestation_1)
 
     yield from run_attester_slashing_processing(spec, state, attester_slashing, False)
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py b/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py
index 482085fd1..090858a2e 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_crosslinks.py
@@ -96,7 +96,7 @@ def test_single_crosslink_update_from_previous_epoch(spec, state):
     # ensure rewarded
     for index in spec.get_crosslink_committee(
             state,
-            attestation.data.target_checkpoint.epoch,
+            attestation.data.target.epoch,
             attestation.data.crosslink.shard):
         assert crosslink_deltas[0][index] > 0
         assert crosslink_deltas[1][index] == 0
@@ -148,7 +148,7 @@ def test_double_late_crosslink(spec, state):
     # ensure no reward, only penalties for the failed crosslink
     for index in spec.get_crosslink_committee(
             state,
-            attestation_2.data.target_checkpoint.epoch,
+            attestation_2.data.target.epoch,
             attestation_2.data.crosslink.shard):
         assert crosslink_deltas[0][index] == 0
         assert crosslink_deltas[1][index] > 0