diff --git a/Sources/BeaconChain/StateTransition.swift b/Sources/BeaconChain/StateTransition.swift
index 16587eb..7c617bb 100644
--- a/Sources/BeaconChain/StateTransition.swift
+++ b/Sources/BeaconChain/StateTransition.swift
@@ -24,9 +24,10 @@ extension StateTransition {
         eth1data(state: &state, block: block)
         proposerSlashings(state: &state, block: block)
         attesterSlashings(state: &state, block: block)
-        attestations(state: &state, block: block)
-        deposits(state: &state, block: block)
-        voluntaryExits(state: &state, block: block)
+        Attestations.transition(state: &state, block: block)
+        Deposits.transition(state: &state, block: block)
+        VoluntaryExits.transition(state: &state, block: block)
+        Transfers.transition(state: &state, block: block)
     }
 
     static func blockSignature(state: inout BeaconState, block: BeaconBlock) {
@@ -137,167 +138,6 @@ extension StateTransition {
         }
     }
 
-    static func attestations(state: inout BeaconState, block: BeaconBlock) {
-        assert(block.body.attestations.count <= MAX_ATTESTATIONS)
-
-        for attestation in block.body.attestations {
-            assert(attestation.data.slot >= GENESIS_SLOT)
-            assert(attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot)
-            assert(state.slot < attestation.data.slot + SLOTS_PER_EPOCH)
-
-            let e = (attestation.data.slot + 1).toEpoch() >= BeaconChain.getCurrentEpoch(state: state) ? state.justifiedEpoch : state.previousJustifiedEpoch
-            assert(attestation.data.justifiedEpoch == e)
-            assert(attestation.data.justifiedBlockRoot == BeaconChain.getBlockRoot(state: state, slot: attestation.data.justifiedEpoch.startSlot()))
-
-            assert(
-                state.latestCrosslinks[Int(attestation.data.shard)] == attestation.data.latestCrosslink ||
-                state.latestCrosslinks[Int(attestation.data.shard)] == Crosslink(
-                    epoch: attestation.data.slot.toEpoch(),
-                    crosslinkDataRoot: attestation.data.crosslinkDataRoot
-                )
-            )
-
-            assert(attestation.custodyBitfield == Data(repeating: 0, count: 32))
-            assert(attestation.aggregationBitfield != Data(repeating: 0, count: 32))
-
-            let crosslinkCommittee = BeaconChain.crosslinkCommittees(state, at: attestation.data.slot).filter {
-                $0.1 == attestation.data.shard
-            }.first?.0
-
-            for i in 0..<crosslinkCommittee!.count {
-                if BeaconChain.getBitfieldBit(bitfield: attestation.aggregationBitfield, i: i) == 0b0 {
-                    assert(BeaconChain.getBitfieldBit(bitfield: attestation.custodyBitfield, i: i) == 0b1)
-                }
-            }
-
-            let participants = BeaconChain.getAttestationParticipants(
-                state: state,
-                attestationData: attestation.data,
-                bitfield: attestation.aggregationBitfield
-            )
-
-            let custodyBit1Participants = BeaconChain.getAttestationParticipants(
-                state: state,
-                attestationData: attestation.data,
-                bitfield: attestation.custodyBitfield
-            )
-
-            let custodyBit0Participants = participants.filter {
-                !custodyBit1Participants.contains($0)
-            }
-
-            assert(
-                BLS.verify(
-                    pubkeys: [
-                        BLS.aggregate(pubkeys: custodyBit0Participants.map {
-                            return state.validatorRegistry[Int($0)].pubkey
-                        }),
-                        BLS.aggregate(pubkeys: custodyBit1Participants.map {
-                            return state.validatorRegistry[Int($0)].pubkey
-                        })
-                    ],
-                    messages: [
-                        BeaconChain.hashTreeRoot(AttestationDataAndCustodyBit(data: attestation.data, custodyBit: false)),
-                        BeaconChain.hashTreeRoot(AttestationDataAndCustodyBit(data: attestation.data, custodyBit: true))
-                    ],
-                    signature: attestation.aggregateSignature,
-                    domain: state.fork.domain(epoch: attestation.data.slot.toEpoch(), type: .attestation)
-                )
-            )
-
-            assert(attestation.data.crosslinkDataRoot == ZERO_HASH) // @todo remove in phase 1
-
-            state.latestAttestations.append(
-                PendingAttestation(
-                    aggregationBitfield: attestation.aggregationBitfield, data: attestation.data,
-                    custodyBitfield: attestation.custodyBitfield,
-                    inclusionSlot: state.slot
-                )
-            )
-        }
-    }
-
-    static func deposits(state: inout BeaconState, block: BeaconBlock) {
-        assert(block.body.deposits.count <= MAX_DEPOSITS)
-
-        for deposit in block.body.deposits {
-            let serializedDepositData = Data(count: 64) // @todo when we have SSZ
-
-            assert(
-                verifyMerkleBranch(
-                    leaf: BeaconChain.hash(serializedDepositData),
-                    branch: deposit.branch,
-                    depth: Int(DEPOSIT_CONTRACT_TREE_DEPTH),
-                    index: Int(deposit.index),
-                    root: state.latestEth1Data.depositRoot
-                )
-            )
-
-            BeaconChain.processDeposit(
-                state: &state,
-                deposit: deposit
-            )
-
-            state.depositIndex += 1
-        }
-    }
-
-    static func voluntaryExits(state: inout BeaconState, block: BeaconBlock) {
-        assert(block.body.voluntaryExits.count <= MAX_VOLUNTARY_EXITS)
-
-        for exit in block.body.voluntaryExits {
-            let validator = state.validatorRegistry[Int(exit.validatorIndex)]
-
-            let epoch = BeaconChain.getCurrentEpoch(state: state)
-            assert(validator.exitEpoch > epoch.delayedActivationExitEpoch())
-            assert(epoch >= exit.epoch)
-
-            assert(
-                BLS.verify(
-                    pubkey: validator.pubkey,
-                    message: BeaconChain.signedRoot(exit, field: "signature"),
-                    signature: exit.signature,
-                    domain: state.fork.domain(epoch: exit.epoch, type: .exit)
-                )
-            )
-
-            state.validatorRegistry[Int(exit.validatorIndex)].initiatedExit = true
-        }
-    }
-
-    static func transfers(state: inout BeaconState, block: BeaconBlock) {
-        assert(block.body.transfers.count <= MAX_TRANSFERS)
-
-        for transfer in block.body.transfers {
-            assert(state.validatorBalances[Int(transfer.from)] >= transfer.amount)
-            assert(state.validatorBalances[Int(transfer.from)] >= transfer.fee)
-            assert(
-                state.validatorBalances[Int(transfer.from)] == transfer.amount + transfer.fee
-                || state.validatorBalances[Int(transfer.from)] >= transfer.amount + transfer.fee + MIN_DEPOSIT_AMOUNT
-            )
-
-            assert(state.slot == transfer.slot)
-            assert(
-                BeaconChain.getCurrentEpoch(state: state) >= state.validatorRegistry[Int(transfer.from)].withdrawableEpoch
-                || state.validatorRegistry[Int(transfer.from)].activationEpoch == FAR_FUTURE_EPOCH
-            )
-            assert(state.validatorRegistry[Int(transfer.from)].withdrawalCredentials == BLS_WITHDRAWAL_PREFIX_BYTE + BeaconChain.hash(transfer.pubkey).suffix(from: 1))
-
-            assert(
-                BLS.verify(
-                    pubkey: transfer.pubkey,
-                    message: BeaconChain.signedRoot(transfer, field: "signature"),
-                    signature: transfer.signature,
-                    domain: state.fork.domain(epoch: transfer.slot.toEpoch(), type: .transfer)
-                )
-            )
-
-            state.validatorBalances[Int(transfer.from)] -= transfer.amount + transfer.fee
-            state.validatorBalances[Int(transfer.to)] += transfer.amount
-            state.validatorBalances[Int(BeaconChain.getBeaconProposerIndex(state: state, slot: state.slot))] += transfer.fee
-        }
-    }
-
     static func verifyMerkleBranch(leaf: Bytes32, branch: [Bytes32], depth: Int, index: Int, root: Bytes32) -> Bool {
         var value = leaf
         for i in 0..<depth {
diff --git a/Sources/BeaconChain/StateTransitions/Blocks/Attestations.swift b/Sources/BeaconChain/StateTransitions/Blocks/Attestations.swift
new file mode 100644
index 0000000..66bacb8
--- /dev/null
+++ b/Sources/BeaconChain/StateTransitions/Blocks/Attestations.swift
@@ -0,0 +1,84 @@
+import Foundation
+
+class Attestations: BlockTransitions {
+
+    static func transition(state: inout BeaconState, block: BeaconBlock) {
+        assert(block.body.attestations.count <= MAX_ATTESTATIONS)
+
+        for attestation in block.body.attestations {
+            assert(attestation.data.slot >= GENESIS_SLOT)
+            assert(attestation.data.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot)
+            assert(state.slot < attestation.data.slot + SLOTS_PER_EPOCH)
+
+            let e = (attestation.data.slot + 1).toEpoch() >= BeaconChain.getCurrentEpoch(state: state) ? state.justifiedEpoch : state.previousJustifiedEpoch
+            assert(attestation.data.justifiedEpoch == e)
+            assert(attestation.data.justifiedBlockRoot == BeaconChain.getBlockRoot(state: state, slot: attestation.data.justifiedEpoch.startSlot()))
+
+            assert(
+                state.latestCrosslinks[Int(attestation.data.shard)] == attestation.data.latestCrosslink ||
+                    state.latestCrosslinks[Int(attestation.data.shard)] == Crosslink(
+                        epoch: attestation.data.slot.toEpoch(),
+                        crosslinkDataRoot: attestation.data.crosslinkDataRoot
+                    )
+            )
+
+            assert(attestation.custodyBitfield == Data(repeating: 0, count: 32))
+            assert(attestation.aggregationBitfield != Data(repeating: 0, count: 32))
+
+            let crosslinkCommittee = BeaconChain.crosslinkCommittees(state, at: attestation.data.slot).filter {
+                $0.1 == attestation.data.shard
+            }.first?.0
+
+            for i in 0..<crosslinkCommittee!.count {
+                if BeaconChain.getBitfieldBit(bitfield: attestation.aggregationBitfield, i: i) == 0b0 {
+                    assert(BeaconChain.getBitfieldBit(bitfield: attestation.custodyBitfield, i: i) == 0b1)
+                }
+            }
+
+            let participants = BeaconChain.getAttestationParticipants(
+                state: state,
+                attestationData: attestation.data,
+                bitfield: attestation.aggregationBitfield
+            )
+
+            let custodyBit1Participants = BeaconChain.getAttestationParticipants(
+                state: state,
+                attestationData: attestation.data,
+                bitfield: attestation.custodyBitfield
+            )
+
+            let custodyBit0Participants = participants.filter {
+                !custodyBit1Participants.contains($0)
+            }
+
+            assert(
+                BLS.verify(
+                    pubkeys: [
+                        BLS.aggregate(pubkeys: custodyBit0Participants.map {
+                            return state.validatorRegistry[Int($0)].pubkey
+                        }),
+                        BLS.aggregate(pubkeys: custodyBit1Participants.map {
+                            return state.validatorRegistry[Int($0)].pubkey
+                        })
+                    ],
+                    messages: [
+                        BeaconChain.hashTreeRoot(AttestationDataAndCustodyBit(data: attestation.data, custodyBit: false)),
+                        BeaconChain.hashTreeRoot(AttestationDataAndCustodyBit(data: attestation.data, custodyBit: true))
+                    ],
+                    signature: attestation.aggregateSignature,
+                    domain: state.fork.domain(epoch: attestation.data.slot.toEpoch(), type: .attestation)
+                )
+            )
+
+            assert(attestation.data.crosslinkDataRoot == ZERO_HASH) // @todo remove in phase 1
+
+            state.latestAttestations.append(
+                PendingAttestation(
+                    aggregationBitfield: attestation.aggregationBitfield, data: attestation.data,
+                    custodyBitfield: attestation.custodyBitfield,
+                    inclusionSlot: state.slot
+                )
+            )
+        }
+    }
+}
diff --git a/Sources/BeaconChain/StateTransitions/Blocks/BlockTransitions.swift b/Sources/BeaconChain/StateTransitions/Blocks/BlockTransitions.swift
new file mode 100644
index 0000000..e6162ce
--- /dev/null
+++ b/Sources/BeaconChain/StateTransitions/Blocks/BlockTransitions.swift
@@ -0,0 +1,6 @@
+import Foundation
+
+protocol BlockTransitions {
+
+    static func transition(state: inout BeaconState, block: BeaconBlock);
+}
diff --git a/Sources/BeaconChain/StateTransitions/Blocks/Deposits.swift b/Sources/BeaconChain/StateTransitions/Blocks/Deposits.swift
new file mode 100644
index 0000000..cc72e9a
--- /dev/null
+++ b/Sources/BeaconChain/StateTransitions/Blocks/Deposits.swift
@@ -0,0 +1,29 @@
+import Foundation
+
+class Deposits: BlockTransitions {
+
+    static func transition(state: inout BeaconState, block: BeaconBlock) {
+        assert(block.body.deposits.count <= MAX_DEPOSITS)
+
+        for deposit in block.body.deposits {
+            let serializedDepositData = Data(count: 64) // @todo when we have SSZ
+
+            assert(
+                StateTransition.verifyMerkleBranch(
+                    leaf: BeaconChain.hash(serializedDepositData),
+                    branch: deposit.branch,
+                    depth: Int(DEPOSIT_CONTRACT_TREE_DEPTH),
+                    index: Int(deposit.index),
+                    root: state.latestEth1Data.depositRoot
+                )
+            )
+
+            BeaconChain.processDeposit(
+                state: &state,
+                deposit: deposit
+            )
+
+            state.depositIndex += 1
+        }
+    }
+}
diff --git a/Sources/BeaconChain/StateTransitions/Blocks/Transfers.swift b/Sources/BeaconChain/StateTransitions/Blocks/Transfers.swift
new file mode 100644
index 0000000..573621d
--- /dev/null
+++ b/Sources/BeaconChain/StateTransitions/Blocks/Transfers.swift
@@ -0,0 +1,37 @@
+import Foundation
+
+class Transfers: BlockTransitions {
+
+    static func transition(state: inout BeaconState, block: BeaconBlock) {
+        assert(block.body.transfers.count <= MAX_TRANSFERS)
+
+        for transfer in block.body.transfers {
+            assert(state.validatorBalances[Int(transfer.from)] >= transfer.amount)
+            assert(state.validatorBalances[Int(transfer.from)] >= transfer.fee)
+            assert(
+                state.validatorBalances[Int(transfer.from)] == transfer.amount + transfer.fee
+                    || state.validatorBalances[Int(transfer.from)] >= transfer.amount + transfer.fee + MIN_DEPOSIT_AMOUNT
+            )
+
+            assert(state.slot == transfer.slot)
+            assert(
+                BeaconChain.getCurrentEpoch(state: state) >= state.validatorRegistry[Int(transfer.from)].withdrawableEpoch
+                    || state.validatorRegistry[Int(transfer.from)].activationEpoch == FAR_FUTURE_EPOCH
+            )
+            assert(state.validatorRegistry[Int(transfer.from)].withdrawalCredentials == BLS_WITHDRAWAL_PREFIX_BYTE + BeaconChain.hash(transfer.pubkey).suffix(from: 1))
+
+            assert(
+                BLS.verify(
+                    pubkey: transfer.pubkey,
+                    message: BeaconChain.signedRoot(transfer, field: "signature"),
+                    signature: transfer.signature,
+                    domain: state.fork.domain(epoch: transfer.slot.toEpoch(), type: .transfer)
+                )
+            )
+
+            state.validatorBalances[Int(transfer.from)] -= transfer.amount + transfer.fee
+            state.validatorBalances[Int(transfer.to)] += transfer.amount
+            state.validatorBalances[Int(BeaconChain.getBeaconProposerIndex(state: state, slot: state.slot))] += transfer.fee
+        }
+    }
+}
diff --git a/Sources/BeaconChain/StateTransitions/Blocks/VoluntaryExits.swift b/Sources/BeaconChain/StateTransitions/Blocks/VoluntaryExits.swift
new file mode 100644
index 0000000..25325c9
--- /dev/null
+++ b/Sources/BeaconChain/StateTransitions/Blocks/VoluntaryExits.swift
@@ -0,0 +1,27 @@
+import Foundation
+
+class VoluntaryExits: BlockTransitions {
+
+    static func transition(state: inout BeaconState, block: BeaconBlock) {
+        assert(block.body.voluntaryExits.count <= MAX_VOLUNTARY_EXITS)
+
+        for exit in block.body.voluntaryExits {
+            let validator = state.validatorRegistry[Int(exit.validatorIndex)]
+
+            let epoch = BeaconChain.getCurrentEpoch(state: state)
+            assert(validator.exitEpoch > epoch.delayedActivationExitEpoch())
+            assert(epoch >= exit.epoch)
+
+            assert(
+                BLS.verify(
+                    pubkey: validator.pubkey,
+                    message: BeaconChain.signedRoot(exit, field: "signature"),
+                    signature: exit.signature,
+                    domain: state.fork.domain(epoch: exit.epoch, type: .exit)
+                )
+            )
+
+            state.validatorRegistry[Int(exit.validatorIndex)].initiatedExit = true
+        }
+    }
+}