diff --git a/blockchain/pool.go b/blockchain/pool.go
index 933089cf..8b932531 100644
--- a/blockchain/pool.go
+++ b/blockchain/pool.go
@@ -52,22 +52,22 @@ type BlockPool struct {
 
 	mtx sync.Mutex
 	// block requests
-	requesters map[int]*bpRequester
-	height     int   // the lowest key in requesters.
-	numPending int32 // number of requests pending assignment or block response
+	requesters map[uint64]*bpRequester
+	height     uint64 // the lowest key in requesters.
+	numPending int32  // number of requests pending assignment or block response
 	// peers
 	peers         map[string]*bpPeer
-	maxPeerHeight int
+	maxPeerHeight uint64
 
 	requestsCh chan<- BlockRequest
 	timeoutsCh chan<- string
 }
 
-func NewBlockPool(start int, requestsCh chan<- BlockRequest, timeoutsCh chan<- string) *BlockPool {
+func NewBlockPool(start uint64, requestsCh chan<- BlockRequest, timeoutsCh chan<- string) *BlockPool {
 	bp := &BlockPool{
 		peers: make(map[string]*bpPeer),
 
-		requesters: make(map[int]*bpRequester),
+		requesters: make(map[uint64]*bpRequester),
 		height:     start,
 		numPending: 0,
 
@@ -132,7 +132,7 @@ func (pool *BlockPool) removeTimedoutPeers() {
 	}
 }
 
-func (pool *BlockPool) GetStatus() (height int, numPending int32, lenRequesters int) {
+func (pool *BlockPool) GetStatus() (height uint64, numPending int32, lenRequesters int) {
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
@@ -195,7 +195,7 @@ func (pool *BlockPool) PopRequest() {
 
 // Invalidates the block at pool.height,
 // Remove the peer and redo request from others.
-func (pool *BlockPool) RedoRequest(height int) {
+func (pool *BlockPool) RedoRequest(height uint64) {
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
@@ -233,14 +233,14 @@ func (pool *BlockPool) AddBlock(peerID string, block *types.Block, blockSize int
 }
 
 // MaxPeerHeight returns the highest height reported by a peer.
-func (pool *BlockPool) MaxPeerHeight() int {
+func (pool *BlockPool) MaxPeerHeight() uint64 {
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 	return pool.maxPeerHeight
 }
 
 // Sets the peer's alleged blockchain height.
-func (pool *BlockPool) SetPeerHeight(peerID string, height int) {
+func (pool *BlockPool) SetPeerHeight(peerID string, height uint64) {
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
@@ -279,7 +279,7 @@ func (pool *BlockPool) removePeer(peerID string) {
 
 // Pick an available peer with at least the given minHeight.
 // If no peers are available, returns nil.
-func (pool *BlockPool) pickIncrAvailablePeer(minHeight int) *bpPeer {
+func (pool *BlockPool) pickIncrAvailablePeer(minHeight uint64) *bpPeer {
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
@@ -304,7 +304,7 @@ func (pool *BlockPool) makeNextRequester() {
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
-	nextHeight := pool.height + len(pool.requesters)
+	nextHeight := pool.height + pool.requestersLen()
 	request := newBPRequester(pool, nextHeight)
 	// request.SetLogger(pool.Logger.With("height", nextHeight))
 
@@ -317,7 +317,11 @@ func (pool *BlockPool) makeNextRequester() {
 	}
 }
 
-func (pool *BlockPool) sendRequest(height int, peerID string) {
+func (pool *BlockPool) requestersLen() uint64 {
+	return uint64(len(pool.requesters))
+}
+
+func (pool *BlockPool) sendRequest(height uint64, peerID string) {
 	if !pool.IsRunning() {
 		return
 	}
@@ -337,7 +341,8 @@ func (pool *BlockPool) debug() string {
 	defer pool.mtx.Unlock()
 
 	str := ""
-	for h := pool.height; h < pool.height+len(pool.requesters); h++ {
+	nextHeight := pool.height + pool.requestersLen()
+	for h := pool.height; h < nextHeight; h++ {
 		if pool.requesters[h] == nil {
 			str += cmn.Fmt("H(%v):X ", h)
 		} else {
@@ -355,7 +360,7 @@ type bpPeer struct {
 	id          string
 	recvMonitor *flow.Monitor
 
-	height     int
+	height     uint64
 	numPending int32
 	timeout    *time.Timer
 	didTimeout bool
@@ -363,7 +368,7 @@ type bpPeer struct {
 	logger log.Logger
 }
 
-func newBPPeer(pool *BlockPool, peerID string, height int) *bpPeer {
+func newBPPeer(pool *BlockPool, peerID string, height uint64) *bpPeer {
 	peer := &bpPeer{
 		pool:       pool,
 		id:         peerID,
@@ -424,7 +429,7 @@ func (peer *bpPeer) onTimeout() {
 type bpRequester struct {
 	cmn.BaseService
 	pool       *BlockPool
-	height     int
+	height     uint64
 	gotBlockCh chan struct{}
 	redoCh     chan struct{}
 
@@ -433,7 +438,7 @@ type bpRequester struct {
 	block  *types.Block
 }
 
-func newBPRequester(pool *BlockPool, height int) *bpRequester {
+func newBPRequester(pool *BlockPool, height uint64) *bpRequester {
 	bpr := &bpRequester{
 		pool:       pool,
 		height:     height,
@@ -545,6 +550,6 @@ OUTER_LOOP:
 //-------------------------------------
 
 type BlockRequest struct {
-	Height int
+	Height uint64
 	PeerID string
 }
diff --git a/blockchain/pool_test.go b/blockchain/pool_test.go
index 42454307..6f9a43b1 100644
--- a/blockchain/pool_test.go
+++ b/blockchain/pool_test.go
@@ -16,21 +16,21 @@ func init() {
 
 type testPeer struct {
 	id     string
-	height int
+	height uint64
 }
 
-func makePeers(numPeers int, minHeight, maxHeight int) map[string]testPeer {
+func makePeers(numPeers int, minHeight, maxHeight uint64) map[string]testPeer {
 	peers := make(map[string]testPeer, numPeers)
 	for i := 0; i < numPeers; i++ {
 		peerID := cmn.RandStr(12)
-		height := minHeight + rand.Intn(maxHeight-minHeight)
+		height := minHeight + uint64(rand.Intn(int(maxHeight-minHeight)))
 		peers[peerID] = testPeer{peerID, height}
 	}
 	return peers
 }
 
 func TestBasic(t *testing.T) {
-	start := 42
+	start := uint64(42)
 	peers := makePeers(10, start+1, 1000)
 	timeoutsCh := make(chan string, 100)
 	requestsCh := make(chan BlockRequest, 100)
@@ -87,7 +87,7 @@ func TestBasic(t *testing.T) {
 }
 
 func TestTimeout(t *testing.T) {
-	start := 42
+	start := uint64(42)
 	peers := makePeers(10, start+1, 1000)
 	timeoutsCh := make(chan string, 100)
 	requestsCh := make(chan BlockRequest, 100)
diff --git a/blockchain/reactor.go b/blockchain/reactor.go
index 2646f6d8..828ec73e 100644
--- a/blockchain/reactor.go
+++ b/blockchain/reactor.go
@@ -347,7 +347,7 @@ func DecodeMessage(bz []byte, maxSize int) (msgType byte, msg BlockchainMessage,
 //-------------------------------------
 
 type bcBlockRequestMessage struct {
-	Height int
+	Height uint64
 }
 
 func (m *bcBlockRequestMessage) String() string {
@@ -355,7 +355,7 @@ func (m *bcBlockRequestMessage) String() string {
 }
 
 type bcNoBlockResponseMessage struct {
-	Height int
+	Height uint64
 }
 
 func (brm *bcNoBlockResponseMessage) String() string {
@@ -376,7 +376,7 @@ func (m *bcBlockResponseMessage) String() string {
 //-------------------------------------
 
 type bcStatusRequestMessage struct {
-	Height int
+	Height uint64
 }
 
 func (m *bcStatusRequestMessage) String() string {
@@ -386,7 +386,7 @@ func (m *bcStatusRequestMessage) String() string {
 //-------------------------------------
 
 type bcStatusResponseMessage struct {
-	Height int
+	Height uint64
 }
 
 func (m *bcStatusResponseMessage) String() string {
diff --git a/blockchain/reactor_test.go b/blockchain/reactor_test.go
index 584aadf3..d4ada4f7 100644
--- a/blockchain/reactor_test.go
+++ b/blockchain/reactor_test.go
@@ -14,7 +14,7 @@ import (
 	"github.com/tendermint/tendermint/types"
 )
 
-func newBlockchainReactor(maxBlockHeight int) *BlockchainReactor {
+func newBlockchainReactor(maxBlockHeight uint64) *BlockchainReactor {
 	logger := log.TestingLogger()
 	config := cfg.ResetTestRoot("blockchain_reactor_test")
 
@@ -34,7 +34,7 @@ func newBlockchainReactor(maxBlockHeight int) *BlockchainReactor {
 	bcReactor.Switch = p2p.NewSwitch(cfg.DefaultP2PConfig())
 
 	// Lastly: let's add some blocks in
-	for blockHeight := 1; blockHeight <= maxBlockHeight; blockHeight++ {
+	for blockHeight := uint64(1); blockHeight <= maxBlockHeight; blockHeight++ {
 		firstBlock := makeBlock(blockHeight, state)
 		secondBlock := makeBlock(blockHeight+1, state)
 		firstParts := firstBlock.MakePartSet(state.Params.BlockGossipParams.BlockPartSizeBytes)
@@ -45,7 +45,7 @@ func newBlockchainReactor(maxBlockHeight int) *BlockchainReactor {
 }
 
 func TestNoBlockMessageResponse(t *testing.T) {
-	maxBlockHeight := 20
+	maxBlockHeight := uint64(20)
 
 	bcr := newBlockchainReactor(maxBlockHeight)
 	bcr.Start()
@@ -58,7 +58,7 @@ func TestNoBlockMessageResponse(t *testing.T) {
 	chID := byte(0x01)
 
 	tests := []struct {
-		height   int
+		height   uint64
 		existent bool
 	}{
 		{maxBlockHeight + 2, false},
@@ -93,19 +93,19 @@ func TestNoBlockMessageResponse(t *testing.T) {
 //----------------------------------------------
 // utility funcs
 
-func makeTxs(blockNumber int) (txs []types.Tx) {
+func makeTxs(height uint64) (txs []types.Tx) {
 	for i := 0; i < 10; i++ {
-		txs = append(txs, types.Tx([]byte{byte(blockNumber), byte(i)}))
+		txs = append(txs, types.Tx([]byte{byte(height), byte(i)}))
 	}
 	return txs
 }
 
-func makeBlock(blockNumber int, state *sm.State) *types.Block {
+func makeBlock(height uint64, state *sm.State) *types.Block {
 	prevHash := state.LastBlockID.Hash
 	prevParts := types.PartSetHeader{}
 	valHash := state.Validators.Hash()
 	prevBlockID := types.BlockID{prevHash, prevParts}
-	block, _ := types.MakeBlock(blockNumber, "test_chain", makeTxs(blockNumber),
+	block, _ := types.MakeBlock(height, "test_chain", makeTxs(height),
 		new(types.Commit), prevBlockID, valHash, state.AppHash, state.Params.BlockGossipParams.BlockPartSizeBytes)
 	return block
 }
diff --git a/blockchain/store.go b/blockchain/store.go
index bcd10856..8ab16748 100644
--- a/blockchain/store.go
+++ b/blockchain/store.go
@@ -7,7 +7,7 @@ import (
 	"io"
 	"sync"
 
-	"github.com/tendermint/go-wire"
+	wire "github.com/tendermint/go-wire"
 	"github.com/tendermint/tendermint/types"
 	cmn "github.com/tendermint/tmlibs/common"
 	dbm "github.com/tendermint/tmlibs/db"
@@ -32,7 +32,7 @@ type BlockStore struct {
 	db dbm.DB
 
 	mtx    sync.RWMutex
-	height int
+	height uint64
 }
 
 func NewBlockStore(db dbm.DB) *BlockStore {
@@ -44,7 +44,7 @@ func NewBlockStore(db dbm.DB) *BlockStore {
 }
 
 // Height() returns the last known contiguous block height.
-func (bs *BlockStore) Height() int {
+func (bs *BlockStore) Height() uint64 {
 	bs.mtx.RLock()
 	defer bs.mtx.RUnlock()
 	return bs.height
@@ -58,7 +58,7 @@ func (bs *BlockStore) GetReader(key []byte) io.Reader {
 	return bytes.NewReader(bytez)
 }
 
-func (bs *BlockStore) LoadBlock(height int) *types.Block {
+func (bs *BlockStore) LoadBlock(height uint64) *types.Block {
 	var n int
 	var err error
 	r := bs.GetReader(calcBlockMetaKey(height))
@@ -81,7 +81,7 @@ func (bs *BlockStore) LoadBlock(height int) *types.Block {
 	return block
 }
 
-func (bs *BlockStore) LoadBlockPart(height int, index int) *types.Part {
+func (bs *BlockStore) LoadBlockPart(height uint64, index int) *types.Part {
 	var n int
 	var err error
 	r := bs.GetReader(calcBlockPartKey(height, index))
@@ -95,7 +95,7 @@ func (bs *BlockStore) LoadBlockPart(height int, index int) *types.Part {
 	return part
 }
 
-func (bs *BlockStore) LoadBlockMeta(height int) *types.BlockMeta {
+func (bs *BlockStore) LoadBlockMeta(height uint64) *types.BlockMeta {
 	var n int
 	var err error
 	r := bs.GetReader(calcBlockMetaKey(height))
@@ -111,7 +111,7 @@ func (bs *BlockStore) LoadBlockMeta(height int) *types.BlockMeta {
 
 // The +2/3 and other Precommit-votes for block at `height`.
 // This Commit comes from block.LastCommit for `height+1`.
-func (bs *BlockStore) LoadBlockCommit(height int) *types.Commit {
+func (bs *BlockStore) LoadBlockCommit(height uint64) *types.Commit {
 	var n int
 	var err error
 	r := bs.GetReader(calcBlockCommitKey(height))
@@ -126,7 +126,7 @@ func (bs *BlockStore) LoadBlockCommit(height int) *types.Commit {
 }
 
 // NOTE: the Precommit-vote heights are for the block at `height`
-func (bs *BlockStore) LoadSeenCommit(height int) *types.Commit {
+func (bs *BlockStore) LoadSeenCommit(height uint64) *types.Commit {
 	var n int
 	var err error
 	r := bs.GetReader(calcSeenCommitKey(height))
@@ -185,7 +185,7 @@ func (bs *BlockStore) SaveBlock(block *types.Block, blockParts *types.PartSet, s
 	bs.db.SetSync(nil, nil)
 }
 
-func (bs *BlockStore) saveBlockPart(height int, index int, part *types.Part) {
+func (bs *BlockStore) saveBlockPart(height uint64, index int, part *types.Part) {
 	if height != bs.Height()+1 {
 		cmn.PanicSanity(cmn.Fmt("BlockStore can only save contiguous blocks. Wanted %v, got %v", bs.Height()+1, height))
 	}
@@ -195,19 +195,19 @@ func (bs *BlockStore) saveBlockPart(height int, index int, part *types.Part) {
 
 //-----------------------------------------------------------------------------
 
-func calcBlockMetaKey(height int) []byte {
+func calcBlockMetaKey(height uint64) []byte {
 	return []byte(fmt.Sprintf("H:%v", height))
 }
 
-func calcBlockPartKey(height int, partIndex int) []byte {
+func calcBlockPartKey(height uint64, partIndex int) []byte {
 	return []byte(fmt.Sprintf("P:%v:%v", height, partIndex))
 }
 
-func calcBlockCommitKey(height int) []byte {
+func calcBlockCommitKey(height uint64) []byte {
 	return []byte(fmt.Sprintf("C:%v", height))
 }
 
-func calcSeenCommitKey(height int) []byte {
+func calcSeenCommitKey(height uint64) []byte {
 	return []byte(fmt.Sprintf("SC:%v", height))
 }
 
@@ -216,7 +216,7 @@ func calcSeenCommitKey(height int) []byte {
 var blockStoreKey = []byte("blockStore")
 
 type BlockStoreStateJSON struct {
-	Height int
+	Height uint64
 }
 
 func (bsj BlockStoreStateJSON) Save(db dbm.DB) {
diff --git a/consensus/byzantine_test.go b/consensus/byzantine_test.go
index 5d0d3b55..6f73fd56 100644
--- a/consensus/byzantine_test.go
+++ b/consensus/byzantine_test.go
@@ -48,12 +48,12 @@ func TestByzantine(t *testing.T) {
 		if i == 0 {
 			css[i].privValidator = NewByzantinePrivValidator(css[i].privValidator)
 			// make byzantine
-			css[i].decideProposal = func(j int) func(int, int) {
-				return func(height, round int) {
+			css[i].decideProposal = func(j int) func(uint64, int) {
+				return func(height uint64, round int) {
 					byzantineDecideProposalFunc(t, height, round, css[j], switches[j])
 				}
 			}(i)
-			css[i].doPrevote = func(height, round int) {}
+			css[i].doPrevote = func(height uint64, round int) {}
 		}
 
 		eventBus := types.NewEventBus()
@@ -162,7 +162,7 @@ func TestByzantine(t *testing.T) {
 //-------------------------------
 // byzantine consensus functions
 
-func byzantineDecideProposalFunc(t *testing.T, height, round int, cs *ConsensusState, sw *p2p.Switch) {
+func byzantineDecideProposalFunc(t *testing.T, height uint64, round int, cs *ConsensusState, sw *p2p.Switch) {
 	// byzantine user should create two proposals and try to split the vote.
 	// Avoid sending on internalMsgQueue and running consensus state.
 
@@ -197,7 +197,7 @@ func byzantineDecideProposalFunc(t *testing.T, height, round int, cs *ConsensusS
 	}
 }
 
-func sendProposalAndParts(height, round int, cs *ConsensusState, peer p2p.Peer, proposal *types.Proposal, blockHash []byte, parts *types.PartSet) {
+func sendProposalAndParts(height uint64, round int, cs *ConsensusState, peer p2p.Peer, proposal *types.Proposal, blockHash []byte, parts *types.PartSet) {
 	// proposal
 	msg := &ProposalMessage{Proposal: proposal}
 	peer.Send(DataChannel, struct{ ConsensusMessage }{msg})
diff --git a/consensus/common_test.go b/consensus/common_test.go
index 8d2fafbb..67a72075 100644
--- a/consensus/common_test.go
+++ b/consensus/common_test.go
@@ -54,7 +54,7 @@ func ResetConfig(name string) *cfg.Config {
 
 type validatorStub struct {
 	Index  int // Validator index. NOTE: we don't assume validator set changes.
-	Height int
+	Height uint64
 	Round  int
 	types.PrivValidator
 }
@@ -113,13 +113,13 @@ func incrementRound(vss ...*validatorStub) {
 //-------------------------------------------------------------------------------
 // Functions for transitioning the consensus state
 
-func startTestRound(cs *ConsensusState, height, round int) {
+func startTestRound(cs *ConsensusState, height uint64, round int) {
 	cs.enterNewRound(height, round)
 	cs.startRoutines(0)
 }
 
 // Create proposal block from cs1 but sign it with vs
-func decideProposal(cs1 *ConsensusState, vs *validatorStub, height, round int) (proposal *types.Proposal, block *types.Block) {
+func decideProposal(cs1 *ConsensusState, vs *validatorStub, height uint64, round int) (proposal *types.Proposal, block *types.Block) {
 	block, blockParts := cs1.createProposalBlock()
 	if block == nil { // on error
 		panic("error creating proposal block")
diff --git a/consensus/reactor.go b/consensus/reactor.go
index 38cf8b94..3502f573 100644
--- a/consensus/reactor.go
+++ b/consensus/reactor.go
@@ -861,7 +861,7 @@ func (ps *PeerState) GetRoundState() *cstypes.PeerRoundState {
 
 // GetHeight returns an atomic snapshot of the PeerRoundState's height
 // used by the mempool to ensure peers are caught up before broadcasting new txs
-func (ps *PeerState) GetHeight() int {
+func (ps *PeerState) GetHeight() uint64 {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 	return ps.PeerRoundState.Height
@@ -900,7 +900,7 @@ func (ps *PeerState) InitProposalBlockParts(partsHeader types.PartSetHeader) {
 }
 
 // SetHasProposalBlockPart sets the given block part index as known for the peer.
-func (ps *PeerState) SetHasProposalBlockPart(height int, round int, index int) {
+func (ps *PeerState) SetHasProposalBlockPart(height uint64, round int, index int) {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 
@@ -951,7 +951,7 @@ func (ps *PeerState) PickVoteToSend(votes types.VoteSetReader) (vote *types.Vote
 	return nil, false
 }
 
-func (ps *PeerState) getVoteBitArray(height, round int, type_ byte) *cmn.BitArray {
+func (ps *PeerState) getVoteBitArray(height uint64, round int, type_ byte) *cmn.BitArray {
 	if !types.IsVoteTypeValid(type_) {
 		return nil
 	}
@@ -998,7 +998,7 @@ func (ps *PeerState) getVoteBitArray(height, round int, type_ byte) *cmn.BitArra
 }
 
 // 'round': A round for which we have a +2/3 commit.
-func (ps *PeerState) ensureCatchupCommitRound(height, round int, numValidators int) {
+func (ps *PeerState) ensureCatchupCommitRound(height uint64, round int, numValidators int) {
 	if ps.Height != height {
 		return
 	}
@@ -1024,13 +1024,13 @@ func (ps *PeerState) ensureCatchupCommitRound(height, round int, numValidators i
 // what votes this peer has received.
 // NOTE: It's important to make sure that numValidators actually matches
 // what the node sees as the number of validators for height.
-func (ps *PeerState) EnsureVoteBitArrays(height int, numValidators int) {
+func (ps *PeerState) EnsureVoteBitArrays(height uint64, numValidators int) {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 	ps.ensureVoteBitArrays(height, numValidators)
 }
 
-func (ps *PeerState) ensureVoteBitArrays(height int, numValidators int) {
+func (ps *PeerState) ensureVoteBitArrays(height uint64, numValidators int) {
 	if ps.Height == height {
 		if ps.Prevotes == nil {
 			ps.Prevotes = cmn.NewBitArray(numValidators)
@@ -1059,7 +1059,7 @@ func (ps *PeerState) SetHasVote(vote *types.Vote) {
 	ps.setHasVote(vote.Height, vote.Round, vote.Type, vote.ValidatorIndex)
 }
 
-func (ps *PeerState) setHasVote(height int, round int, type_ byte, index int) {
+func (ps *PeerState) setHasVote(height uint64, round int, type_ byte, index int) {
 	logger := ps.logger.With("peerH/R", cmn.Fmt("%d/%d", ps.Height, ps.Round), "H/R", cmn.Fmt("%d/%d", height, round))
 	logger.Debug("setHasVote", "type", type_, "index", index)
 
@@ -1253,7 +1253,7 @@ func DecodeMessage(bz []byte) (msgType byte, msg ConsensusMessage, err error) {
 // NewRoundStepMessage is sent for every step taken in the ConsensusState.
 // For every height/round/step transition
 type NewRoundStepMessage struct {
-	Height                int
+	Height                uint64
 	Round                 int
 	Step                  cstypes.RoundStepType
 	SecondsSinceStartTime int
@@ -1270,7 +1270,7 @@ func (m *NewRoundStepMessage) String() string {
 
 // CommitStepMessage is sent when a block is committed.
 type CommitStepMessage struct {
-	Height           int
+	Height           uint64
 	BlockPartsHeader types.PartSetHeader
 	BlockParts       *cmn.BitArray
 }
@@ -1296,7 +1296,7 @@ func (m *ProposalMessage) String() string {
 
 // ProposalPOLMessage is sent when a previous proposal is re-proposed.
 type ProposalPOLMessage struct {
-	Height           int
+	Height           uint64
 	ProposalPOLRound int
 	ProposalPOL      *cmn.BitArray
 }
@@ -1310,7 +1310,7 @@ func (m *ProposalPOLMessage) String() string {
 
 // BlockPartMessage is sent when gossipping a piece of the proposed block.
 type BlockPartMessage struct {
-	Height int
+	Height uint64
 	Round  int
 	Part   *types.Part
 }
@@ -1336,7 +1336,7 @@ func (m *VoteMessage) String() string {
 
 // HasVoteMessage is sent to indicate that a particular vote has been received.
 type HasVoteMessage struct {
-	Height int
+	Height uint64
 	Round  int
 	Type   byte
 	Index  int
@@ -1351,7 +1351,7 @@ func (m *HasVoteMessage) String() string {
 
 // VoteSetMaj23Message is sent to indicate that a given BlockID has seen +2/3 votes.
 type VoteSetMaj23Message struct {
-	Height  int
+	Height  uint64
 	Round   int
 	Type    byte
 	BlockID types.BlockID
@@ -1366,7 +1366,7 @@ func (m *VoteSetMaj23Message) String() string {
 
 // VoteSetBitsMessage is sent to communicate the bit-array of votes seen for the BlockID.
 type VoteSetBitsMessage struct {
-	Height  int
+	Height  uint64
 	Round   int
 	Type    byte
 	BlockID types.BlockID
diff --git a/consensus/replay.go b/consensus/replay.go
index da68df51..8f7f99f1 100644
--- a/consensus/replay.go
+++ b/consensus/replay.go
@@ -90,7 +90,7 @@ func (cs *ConsensusState) readReplayMessage(msg *TimedWALMessage, newStepCh chan
 
 // replay only those messages since the last block.
 // timeoutRoutine should run concurrently to read off tickChan
-func (cs *ConsensusState) catchupReplay(csHeight int) error {
+func (cs *ConsensusState) catchupReplay(csHeight uint64) error {
 	// set replayMode
 	cs.replayMode = true
 	defer func() { cs.replayMode = false }()
@@ -98,7 +98,7 @@ func (cs *ConsensusState) catchupReplay(csHeight int) error {
 	// Ensure that ENDHEIGHT for this height doesn't exist
 	// NOTE: This is just a sanity check. As far as we know things work fine without it,
 	// and Handshake could reuse ConsensusState if it weren't for this check (since we can crash after writing ENDHEIGHT).
-	gr, found, err := cs.wal.SearchForEndHeight(uint64(csHeight))
+	gr, found, err := cs.wal.SearchForEndHeight(csHeight)
 	if err != nil {
 		return err
 	}
@@ -112,7 +112,7 @@ func (cs *ConsensusState) catchupReplay(csHeight int) error {
 	}
 
 	// Search for last height marker
-	gr, found, err = cs.wal.SearchForEndHeight(uint64(csHeight - 1))
+	gr, found, err = cs.wal.SearchForEndHeight(csHeight - 1)
 	if err == io.EOF {
 		cs.Logger.Error("Replay: wal.group.Search returned EOF", "#ENDHEIGHT", csHeight-1)
 	} else if err != nil {
@@ -151,7 +151,7 @@ func (cs *ConsensusState) catchupReplay(csHeight int) error {
 // Parses marker lines of the form:
 // #ENDHEIGHT: 12345
 /*
-func makeHeightSearchFunc(height int) auto.SearchFunc {
+func makeHeightSearchFunc(height uint64) auto.SearchFunc {
 	return func(line string) (int, error) {
 		line = strings.TrimRight(line, "\n")
 		parts := strings.Split(line, " ")
@@ -205,7 +205,7 @@ func (h *Handshaker) Handshake(proxyApp proxy.AppConns) error {
 		return errors.New(cmn.Fmt("Error calling Info: %v", err))
 	}
 
-	blockHeight := int(res.LastBlockHeight) // XXX: beware overflow
+	blockHeight := res.LastBlockHeight
 	appHash := res.LastBlockAppHash
 
 	h.logger.Info("ABCI Handshake", "appHeight", blockHeight, "appHash", fmt.Sprintf("%X", appHash))
@@ -227,7 +227,7 @@ func (h *Handshaker) Handshake(proxyApp proxy.AppConns) error {
 
 // Replay all blocks since appBlockHeight and ensure the result matches the current state.
 // Returns the final AppHash or an error
-func (h *Handshaker) ReplayBlocks(appHash []byte, appBlockHeight int, proxyApp proxy.AppConns) ([]byte, error) {
+func (h *Handshaker) ReplayBlocks(appHash []byte, appBlockHeight uint64, proxyApp proxy.AppConns) ([]byte, error) {
 
 	storeBlockHeight := h.store.Height()
 	stateBlockHeight := h.state.LastBlockHeight
@@ -302,7 +302,7 @@ func (h *Handshaker) ReplayBlocks(appHash []byte, appBlockHeight int, proxyApp p
 	return nil, nil
 }
 
-func (h *Handshaker) replayBlocks(proxyApp proxy.AppConns, appBlockHeight, storeBlockHeight int, mutateState bool) ([]byte, error) {
+func (h *Handshaker) replayBlocks(proxyApp proxy.AppConns, appBlockHeight, storeBlockHeight uint64, mutateState bool) ([]byte, error) {
 	// App is further behind than it should be, so we need to replay blocks.
 	// We replay all blocks from appBlockHeight+1.
 	//
@@ -338,7 +338,7 @@ func (h *Handshaker) replayBlocks(proxyApp proxy.AppConns, appBlockHeight, store
 }
 
 // ApplyBlock on the proxyApp with the last block.
-func (h *Handshaker) replayBlock(height int, proxyApp proxy.AppConnConsensus) ([]byte, error) {
+func (h *Handshaker) replayBlock(height uint64, proxyApp proxy.AppConnConsensus) ([]byte, error) {
 	mempool := types.MockMempool{}
 
 	block := h.store.LoadBlock(height)
diff --git a/consensus/replay_test.go b/consensus/replay_test.go
index 25fdf4db..1588142d 100644
--- a/consensus/replay_test.go
+++ b/consensus/replay_test.go
@@ -58,7 +58,7 @@ var data_dir = path.Join(cmn.GoPath(), "src/github.com/tendermint/tendermint/con
 // and which ones we need the wal for - then we'd also be able to only flush the
 // wal writer when we need to, instead of with every message.
 
-func startNewConsensusStateAndWaitForBlock(t *testing.T, lastBlockHeight int, blockDB dbm.DB, stateDB dbm.DB) {
+func startNewConsensusStateAndWaitForBlock(t *testing.T, lastBlockHeight uint64, blockDB dbm.DB, stateDB dbm.DB) {
 	logger := log.TestingLogger()
 	state, _ := sm.GetState(stateDB, consensusReplayConfig.GenesisFile())
 	state.SetLogger(logger.With("module", "state"))
@@ -590,21 +590,21 @@ func NewMockBlockStore(config *cfg.Config, params types.ConsensusParams) *mockBl
 	return &mockBlockStore{config, params, nil, nil}
 }
 
-func (bs *mockBlockStore) Height() int                       { return len(bs.chain) }
-func (bs *mockBlockStore) LoadBlock(height int) *types.Block { return bs.chain[height-1] }
-func (bs *mockBlockStore) LoadBlockMeta(height int) *types.BlockMeta {
+func (bs *mockBlockStore) Height() uint64                       { return uint64(len(bs.chain)) }
+func (bs *mockBlockStore) LoadBlock(height uint64) *types.Block { return bs.chain[height-1] }
+func (bs *mockBlockStore) LoadBlockMeta(height uint64) *types.BlockMeta {
 	block := bs.chain[height-1]
 	return &types.BlockMeta{
 		BlockID: types.BlockID{block.Hash(), block.MakePartSet(bs.params.BlockPartSizeBytes).Header()},
 		Header:  block.Header,
 	}
 }
-func (bs *mockBlockStore) LoadBlockPart(height int, index int) *types.Part { return nil }
+func (bs *mockBlockStore) LoadBlockPart(height uint64, index int) *types.Part { return nil }
 func (bs *mockBlockStore) SaveBlock(block *types.Block, blockParts *types.PartSet, seenCommit *types.Commit) {
 }
-func (bs *mockBlockStore) LoadBlockCommit(height int) *types.Commit {
+func (bs *mockBlockStore) LoadBlockCommit(height uint64) *types.Commit {
 	return bs.commits[height-1]
 }
-func (bs *mockBlockStore) LoadSeenCommit(height int) *types.Commit {
+func (bs *mockBlockStore) LoadSeenCommit(height uint64) *types.Commit {
 	return bs.commits[height-1]
 }
diff --git a/consensus/state.go b/consensus/state.go
index d53453bd..8bd31654 100644
--- a/consensus/state.go
+++ b/consensus/state.go
@@ -54,7 +54,7 @@ type msgInfo struct {
 // internally generated messages which may update the state
 type timeoutInfo struct {
 	Duration time.Duration         `json:"duration"`
-	Height   int                   `json:"height"`
+	Height   uint64                `json:"height"`
 	Round    int                   `json:"round"`
 	Step     cstypes.RoundStepType `json:"step"`
 }
@@ -104,8 +104,8 @@ type ConsensusState struct {
 	nSteps int
 
 	// some functions can be overwritten for testing
-	decideProposal func(height, round int)
-	doPrevote      func(height, round int)
+	decideProposal func(height uint64, round int)
+	doPrevote      func(height uint64, round int)
 	setProposal    func(proposal *types.Proposal) error
 
 	// closed when we finish shutting down
@@ -179,7 +179,7 @@ func (cs *ConsensusState) getRoundState() *cstypes.RoundState {
 }
 
 // GetValidators returns a copy of the current validators.
-func (cs *ConsensusState) GetValidators() (int, []*types.Validator) {
+func (cs *ConsensusState) GetValidators() (uint64, []*types.Validator) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	return cs.state.LastBlockHeight, cs.state.Validators.Copy().Validators
@@ -200,7 +200,7 @@ func (cs *ConsensusState) SetTimeoutTicker(timeoutTicker TimeoutTicker) {
 }
 
 // LoadCommit loads the commit for a given height.
-func (cs *ConsensusState) LoadCommit(height int) *types.Commit {
+func (cs *ConsensusState) LoadCommit(height uint64) *types.Commit {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if height == cs.blockStore.Height() {
@@ -331,7 +331,7 @@ func (cs *ConsensusState) SetProposal(proposal *types.Proposal, peerKey string)
 }
 
 // AddProposalBlockPart inputs a part of the proposal block.
-func (cs *ConsensusState) AddProposalBlockPart(height, round int, part *types.Part, peerKey string) error {
+func (cs *ConsensusState) AddProposalBlockPart(height uint64, round int, part *types.Part, peerKey string) error {
 
 	if peerKey == "" {
 		cs.internalMsgQueue <- msgInfo{&BlockPartMessage{height, round, part}, ""}
@@ -360,7 +360,7 @@ func (cs *ConsensusState) SetProposalAndBlock(proposal *types.Proposal, block *t
 //------------------------------------------------------------
 // internal functions for managing the state
 
-func (cs *ConsensusState) updateHeight(height int) {
+func (cs *ConsensusState) updateHeight(height uint64) {
 	cs.Height = height
 }
 
@@ -377,7 +377,7 @@ func (cs *ConsensusState) scheduleRound0(rs *cstypes.RoundState) {
 }
 
 // Attempt to schedule a timeout (by sending timeoutInfo on the tickChan)
-func (cs *ConsensusState) scheduleTimeout(duration time.Duration, height, round int, step cstypes.RoundStepType) {
+func (cs *ConsensusState) scheduleTimeout(duration time.Duration, height uint64, round int, step cstypes.RoundStepType) {
 	cs.timeoutTicker.ScheduleTimeout(timeoutInfo{duration, height, round, step})
 }
 
@@ -627,7 +627,7 @@ func (cs *ConsensusState) handleTimeout(ti timeoutInfo, rs cstypes.RoundState) {
 
 }
 
-func (cs *ConsensusState) handleTxsAvailable(height int) {
+func (cs *ConsensusState) handleTxsAvailable(height uint64) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	// we only need to do this for round 0
@@ -644,7 +644,7 @@ func (cs *ConsensusState) handleTxsAvailable(height int) {
 // Enter: +2/3 precommits for nil at (height,round-1)
 // Enter: +2/3 prevotes any or +2/3 precommits for block or any from (height, round)
 // NOTE: cs.StartTime was already set for height.
-func (cs *ConsensusState) enterNewRound(height int, round int) {
+func (cs *ConsensusState) enterNewRound(height uint64, round int) {
 	if cs.Height != height || round < cs.Round || (cs.Round == round && cs.Step != cstypes.RoundStepNewHeight) {
 		cs.Logger.Debug(cmn.Fmt("enterNewRound(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
 		return
@@ -697,7 +697,7 @@ func (cs *ConsensusState) enterNewRound(height int, round int) {
 
 // needProofBlock returns true on the first height (so the genesis app hash is signed right away)
 // and where the last block (height-1) caused the app hash to change
-func (cs *ConsensusState) needProofBlock(height int) bool {
+func (cs *ConsensusState) needProofBlock(height uint64) bool {
 	if height == 1 {
 		return true
 	}
@@ -706,7 +706,7 @@ func (cs *ConsensusState) needProofBlock(height int) bool {
 	return !bytes.Equal(cs.state.AppHash, lastBlockMeta.Header.AppHash)
 }
 
-func (cs *ConsensusState) proposalHeartbeat(height, round int) {
+func (cs *ConsensusState) proposalHeartbeat(height uint64, round int) {
 	counter := 0
 	addr := cs.privValidator.GetAddress()
 	valIndex, v := cs.Validators.GetByAddress(addr)
@@ -738,7 +738,7 @@ func (cs *ConsensusState) proposalHeartbeat(height, round int) {
 // Enter (CreateEmptyBlocks): from enterNewRound(height,round)
 // Enter (CreateEmptyBlocks, CreateEmptyBlocksInterval > 0 ): after enterNewRound(height,round), after timeout of CreateEmptyBlocksInterval
 // Enter (!CreateEmptyBlocks) : after enterNewRound(height,round), once txs are in the mempool
-func (cs *ConsensusState) enterPropose(height int, round int) {
+func (cs *ConsensusState) enterPropose(height uint64, round int) {
 	if cs.Height != height || round < cs.Round || (cs.Round == round && cstypes.RoundStepPropose <= cs.Step) {
 		cs.Logger.Debug(cmn.Fmt("enterPropose(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
 		return
@@ -785,7 +785,7 @@ func (cs *ConsensusState) isProposer() bool {
 	return bytes.Equal(cs.Validators.GetProposer().Address, cs.privValidator.GetAddress())
 }
 
-func (cs *ConsensusState) defaultDecideProposal(height, round int) {
+func (cs *ConsensusState) defaultDecideProposal(height uint64, round int) {
 	var block *types.Block
 	var blockParts *types.PartSet
 
@@ -873,7 +873,7 @@ func (cs *ConsensusState) createProposalBlock() (block *types.Block, blockParts
 // Enter: any +2/3 prevotes for future round.
 // Prevote for LockedBlock if we're locked, or ProposalBlock if valid.
 // Otherwise vote nil.
-func (cs *ConsensusState) enterPrevote(height int, round int) {
+func (cs *ConsensusState) enterPrevote(height uint64, round int) {
 	if cs.Height != height || round < cs.Round || (cs.Round == round && cstypes.RoundStepPrevote <= cs.Step) {
 		cs.Logger.Debug(cmn.Fmt("enterPrevote(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
 		return
@@ -902,7 +902,7 @@ func (cs *ConsensusState) enterPrevote(height int, round int) {
 	// (so we have more time to try and collect +2/3 prevotes for a single block)
 }
 
-func (cs *ConsensusState) defaultDoPrevote(height int, round int) {
+func (cs *ConsensusState) defaultDoPrevote(height uint64, round int) {
 	logger := cs.Logger.With("height", height, "round", round)
 	// If a block is locked, prevote that.
 	if cs.LockedBlock != nil {
@@ -935,7 +935,7 @@ func (cs *ConsensusState) defaultDoPrevote(height int, round int) {
 }
 
 // Enter: any +2/3 prevotes at next round.
-func (cs *ConsensusState) enterPrevoteWait(height int, round int) {
+func (cs *ConsensusState) enterPrevoteWait(height uint64, round int) {
 	if cs.Height != height || round < cs.Round || (cs.Round == round && cstypes.RoundStepPrevoteWait <= cs.Step) {
 		cs.Logger.Debug(cmn.Fmt("enterPrevoteWait(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
 		return
@@ -961,7 +961,7 @@ func (cs *ConsensusState) enterPrevoteWait(height int, round int) {
 // Lock & precommit the ProposalBlock if we have enough prevotes for it (a POL in this round)
 // else, unlock an existing lock and precommit nil if +2/3 of prevotes were nil,
 // else, precommit nil otherwise.
-func (cs *ConsensusState) enterPrecommit(height int, round int) {
+func (cs *ConsensusState) enterPrecommit(height uint64, round int) {
 	if cs.Height != height || round < cs.Round || (cs.Round == round && cstypes.RoundStepPrecommit <= cs.Step) {
 		cs.Logger.Debug(cmn.Fmt("enterPrecommit(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
 		return
@@ -1054,7 +1054,7 @@ func (cs *ConsensusState) enterPrecommit(height int, round int) {
 }
 
 // Enter: any +2/3 precommits for next round.
-func (cs *ConsensusState) enterPrecommitWait(height int, round int) {
+func (cs *ConsensusState) enterPrecommitWait(height uint64, round int) {
 	if cs.Height != height || round < cs.Round || (cs.Round == round && cstypes.RoundStepPrecommitWait <= cs.Step) {
 		cs.Logger.Debug(cmn.Fmt("enterPrecommitWait(%v/%v): Invalid args. Current step: %v/%v/%v", height, round, cs.Height, cs.Round, cs.Step))
 		return
@@ -1076,7 +1076,7 @@ func (cs *ConsensusState) enterPrecommitWait(height int, round int) {
 }
 
 // Enter: +2/3 precommits for block
-func (cs *ConsensusState) enterCommit(height int, commitRound int) {
+func (cs *ConsensusState) enterCommit(height uint64, commitRound int) {
 	if cs.Height != height || cstypes.RoundStepCommit <= cs.Step {
 		cs.Logger.Debug(cmn.Fmt("enterCommit(%v/%v): Invalid args. Current step: %v/%v/%v", height, commitRound, cs.Height, cs.Round, cs.Step))
 		return
@@ -1122,7 +1122,7 @@ func (cs *ConsensusState) enterCommit(height int, commitRound int) {
 }
 
 // If we have the block AND +2/3 commits for it, finalize.
-func (cs *ConsensusState) tryFinalizeCommit(height int) {
+func (cs *ConsensusState) tryFinalizeCommit(height uint64) {
 	if cs.Height != height {
 		cmn.PanicSanity(cmn.Fmt("tryFinalizeCommit() cs.Height: %v vs height: %v", cs.Height, height))
 	}
@@ -1144,7 +1144,7 @@ func (cs *ConsensusState) tryFinalizeCommit(height int) {
 }
 
 // Increment height and goto cstypes.RoundStepNewHeight
-func (cs *ConsensusState) finalizeCommit(height int) {
+func (cs *ConsensusState) finalizeCommit(height uint64) {
 	if cs.Height != height || cs.Step != cstypes.RoundStepCommit {
 		cs.Logger.Debug(cmn.Fmt("finalizeCommit(%v): Invalid args. Current step: %v/%v/%v", height, cs.Height, cs.Round, cs.Step))
 		return
@@ -1193,7 +1193,7 @@ func (cs *ConsensusState) finalizeCommit(height int) {
 	// WAL replay for blocks with an #ENDHEIGHT
 	// As is, ConsensusState should not be started again
 	// until we successfully call ApplyBlock (ie. here or in Handshake after restart)
-	cs.wal.Save(EndHeightMessage{uint64(height)})
+	cs.wal.Save(EndHeightMessage{height})
 
 	fail.Fail() // XXX
 
@@ -1285,7 +1285,7 @@ func (cs *ConsensusState) defaultSetProposal(proposal *types.Proposal) error {
 
 // NOTE: block is not necessarily valid.
 // Asynchronously triggers either enterPrevote (before we timeout of propose) or tryFinalizeCommit, once we have the full block.
-func (cs *ConsensusState) addProposalBlockPart(height int, part *types.Part, verify bool) (added bool, err error) {
+func (cs *ConsensusState) addProposalBlockPart(height uint64, part *types.Part, verify bool) (added bool, err error) {
 	// Blocks might be reused, so round mismatch is OK
 	if cs.Height != height {
 		return false, nil
@@ -1494,7 +1494,7 @@ func (cs *ConsensusState) signAddVote(type_ byte, hash []byte, header types.Part
 
 //---------------------------------------------------------
 
-func CompareHRS(h1, r1 int, s1 cstypes.RoundStepType, h2, r2 int, s2 cstypes.RoundStepType) int {
+func CompareHRS(h1 uint64, r1 int, s1 cstypes.RoundStepType, h2 uint64, r2 int, s2 cstypes.RoundStepType) int {
 	if h1 < h2 {
 		return -1
 	} else if h1 > h2 {
diff --git a/consensus/test_data/many_blocks.cswal b/consensus/test_data/many_blocks.cswal
index ab486b5a..2af0c3cc 100644
Binary files a/consensus/test_data/many_blocks.cswal and b/consensus/test_data/many_blocks.cswal differ
diff --git a/consensus/types/height_vote_set.go b/consensus/types/height_vote_set.go
index 18c1c78a..42541861 100644
--- a/consensus/types/height_vote_set.go
+++ b/consensus/types/height_vote_set.go
@@ -29,7 +29,7 @@ One for their LastCommit round, and another for the official commit round.
 */
 type HeightVoteSet struct {
 	chainID string
-	height  int
+	height  uint64
 	valSet  *types.ValidatorSet
 
 	mtx               sync.Mutex
@@ -38,7 +38,7 @@ type HeightVoteSet struct {
 	peerCatchupRounds map[string][]int     // keys: peer.Key; values: at most 2 rounds
 }
 
-func NewHeightVoteSet(chainID string, height int, valSet *types.ValidatorSet) *HeightVoteSet {
+func NewHeightVoteSet(chainID string, height uint64, valSet *types.ValidatorSet) *HeightVoteSet {
 	hvs := &HeightVoteSet{
 		chainID: chainID,
 	}
@@ -46,7 +46,7 @@ func NewHeightVoteSet(chainID string, height int, valSet *types.ValidatorSet) *H
 	return hvs
 }
 
-func (hvs *HeightVoteSet) Reset(height int, valSet *types.ValidatorSet) {
+func (hvs *HeightVoteSet) Reset(height uint64, valSet *types.ValidatorSet) {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
 
@@ -59,7 +59,7 @@ func (hvs *HeightVoteSet) Reset(height int, valSet *types.ValidatorSet) {
 	hvs.round = 0
 }
 
-func (hvs *HeightVoteSet) Height() int {
+func (hvs *HeightVoteSet) Height() uint64 {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
 	return hvs.height
diff --git a/consensus/types/height_vote_set_test.go b/consensus/types/height_vote_set_test.go
index d5797368..14f66b6a 100644
--- a/consensus/types/height_vote_set_test.go
+++ b/consensus/types/height_vote_set_test.go
@@ -47,7 +47,7 @@ func TestPeerCatchupRounds(t *testing.T) {
 
 }
 
-func makeVoteHR(t *testing.T, height, round int, privVals []*types.PrivValidatorFS, valIndex int) *types.Vote {
+func makeVoteHR(t *testing.T, height uint64, round int, privVals []*types.PrivValidatorFS, valIndex int) *types.Vote {
 	privVal := privVals[valIndex]
 	vote := &types.Vote{
 		ValidatorAddress: privVal.GetAddress(),
diff --git a/consensus/types/reactor.go b/consensus/types/reactor.go
index 2306ee38..dac2bf4e 100644
--- a/consensus/types/reactor.go
+++ b/consensus/types/reactor.go
@@ -13,7 +13,7 @@ import (
 // PeerRoundState contains the known state of a peer.
 // NOTE: Read-only when returned by PeerState.GetRoundState().
 type PeerRoundState struct {
-	Height                   int                 // Height peer is at
+	Height                   uint64              // Height peer is at
 	Round                    int                 // Round peer is at, -1 if unknown.
 	Step                     RoundStepType       // Step peer is at
 	StartTime                time.Time           // Estimated start of round 0 at this height
diff --git a/consensus/types/state.go b/consensus/types/state.go
index 905f7961..c4c91ada 100644
--- a/consensus/types/state.go
+++ b/consensus/types/state.go
@@ -58,7 +58,7 @@ func (rs RoundStepType) String() string {
 // NOTE: Not thread safe. Should only be manipulated by functions downstream
 // of the cs.receiveRoutine
 type RoundState struct {
-	Height             int // Height we are working on
+	Height             uint64 // Height we are working on
 	Round              int
 	Step               RoundStepType
 	StartTime          time.Time
diff --git a/lite/client/provider.go b/lite/client/provider.go
index 9adcc082..2e54ed55 100644
--- a/lite/client/provider.go
+++ b/lite/client/provider.go
@@ -24,7 +24,7 @@ type SignStatusClient interface {
 
 type provider struct {
 	node       SignStatusClient
-	lastHeight int
+	lastHeight uint64
 }
 
 // NewProvider can wrap any rpcclient to expose it as
@@ -68,7 +68,7 @@ func (p *provider) GetByHash(hash []byte) (lite.FullCommit, error) {
 }
 
 // GetByHeight gets the validator set by height
-func (p *provider) GetByHeight(h int) (fc lite.FullCommit, err error) {
+func (p *provider) GetByHeight(h uint64) (fc lite.FullCommit, err error) {
 	commit, err := p.node.Commit(&h)
 	if err != nil {
 		return fc, err
@@ -134,7 +134,7 @@ func (p *provider) seedFromCommit(commit *ctypes.ResultCommit) (fc lite.FullComm
 	return fc, nil
 }
 
-func (p *provider) updateHeight(h int) {
+func (p *provider) updateHeight(h uint64) {
 	if h > p.lastHeight {
 		p.lastHeight = h
 	}
diff --git a/lite/commit.go b/lite/commit.go
index 20eda8f8..2198bbb2 100644
--- a/lite/commit.go
+++ b/lite/commit.go
@@ -42,7 +42,7 @@ func NewFullCommit(commit Commit, vals *types.ValidatorSet) FullCommit {
 }
 
 // Height returns the height of the header.
-func (c Commit) Height() int {
+func (c Commit) Height() uint64 {
 	if c.Header == nil {
 		return 0
 	}
diff --git a/lite/dynamic.go b/lite/dynamic.go
index e05c284d..a9bea700 100644
--- a/lite/dynamic.go
+++ b/lite/dynamic.go
@@ -19,11 +19,11 @@ var _ Certifier = &Dynamic{}
 // going forward.
 type Dynamic struct {
 	cert       *Static
-	lastHeight int
+	lastHeight uint64
 }
 
 // NewDynamic returns a new dynamic certifier.
-func NewDynamic(chainID string, vals *types.ValidatorSet, height int) *Dynamic {
+func NewDynamic(chainID string, vals *types.ValidatorSet, height uint64) *Dynamic {
 	return &Dynamic{
 		cert:       NewStatic(chainID, vals),
 		lastHeight: height,
@@ -46,7 +46,7 @@ func (c *Dynamic) Hash() []byte {
 }
 
 // LastHeight returns the last height of this certifier.
-func (c *Dynamic) LastHeight() int {
+func (c *Dynamic) LastHeight() uint64 {
 	return c.lastHeight
 }
 
diff --git a/lite/dynamic_test.go b/lite/dynamic_test.go
index 87df3f67..998a8a21 100644
--- a/lite/dynamic_test.go
+++ b/lite/dynamic_test.go
@@ -28,7 +28,7 @@ func TestDynamicCert(t *testing.T) {
 	cases := []struct {
 		keys        lite.ValKeys
 		vals        *types.ValidatorSet
-		height      int
+		height      uint64
 		first, last int  // who actually signs
 		proper      bool // true -> expect no error
 		changed     bool // true -> expect validator change error
@@ -70,7 +70,7 @@ func TestDynamicUpdate(t *testing.T) {
 	cert := lite.NewDynamic(chainID, vals, 40)
 
 	// one valid block to give us a sense of time
-	h := 100
+	h := uint64(100)
 	good := keys.GenCommit(chainID, h, nil, vals, []byte("foo"), 0, len(keys))
 	err := cert.Certify(good)
 	require.Nil(err, "%+v", err)
@@ -83,7 +83,7 @@ func TestDynamicUpdate(t *testing.T) {
 	cases := []struct {
 		keys        lite.ValKeys
 		vals        *types.ValidatorSet
-		height      int
+		height      uint64
 		first, last int  // who actually signs
 		proper      bool // true -> expect no error
 		changed     bool // true -> expect too much change error
diff --git a/lite/errors/errors.go b/lite/errors/errors.go
index 96c07539..9b1d5334 100644
--- a/lite/errors/errors.go
+++ b/lite/errors/errors.go
@@ -70,7 +70,7 @@ func ErrNoPathFound() error {
 //--------------------------------------------
 
 type errHeightMismatch struct {
-	h1, h2 int
+	h1, h2 uint64
 }
 
 func (e errHeightMismatch) Error() string {
@@ -87,6 +87,6 @@ func IsHeightMismatchErr(err error) bool {
 }
 
 // ErrHeightMismatch returns an mismatch error with stack-trace
-func ErrHeightMismatch(h1, h2 int) error {
+func ErrHeightMismatch(h1, h2 uint64) error {
 	return errors.WithStack(errHeightMismatch{h1, h2})
 }
diff --git a/lite/files/commit_test.go b/lite/files/commit_test.go
index 97603281..586393e2 100644
--- a/lite/files/commit_test.go
+++ b/lite/files/commit_test.go
@@ -24,7 +24,7 @@ func TestSerializeFullCommits(t *testing.T) {
 	// some constants
 	appHash := []byte("some crazy thing")
 	chainID := "ser-ial"
-	h := 25
+	h := uint64(25)
 
 	// build a fc
 	keys := lite.GenValKeys(5)
diff --git a/lite/files/provider.go b/lite/files/provider.go
index faa68dd9..8eb869ba 100644
--- a/lite/files/provider.go
+++ b/lite/files/provider.go
@@ -60,7 +60,7 @@ func (p *provider) encodeHash(hash []byte) string {
 	return hex.EncodeToString(hash) + Ext
 }
 
-func (p *provider) encodeHeight(h int) string {
+func (p *provider) encodeHeight(h uint64) string {
 	// pad up to 10^12 for height...
 	return fmt.Sprintf("%012d%s", h, Ext)
 }
@@ -88,7 +88,7 @@ func (p *provider) StoreCommit(fc lite.FullCommit) error {
 }
 
 // GetByHeight returns the closest commit with height <= h.
-func (p *provider) GetByHeight(h int) (lite.FullCommit, error) {
+func (p *provider) GetByHeight(h uint64) (lite.FullCommit, error) {
 	// first we look for exact match, then search...
 	path := filepath.Join(p.checkDir, p.encodeHeight(h))
 	fc, err := LoadFullCommit(path)
@@ -109,7 +109,7 @@ func (p *provider) LatestCommit() (fc lite.FullCommit, err error) {
 
 // search for height, looks for a file with highest height < h
 // return certifiers.ErrCommitNotFound() if not there...
-func (p *provider) searchForHeight(h int) (string, error) {
+func (p *provider) searchForHeight(h uint64) (string, error) {
 	d, err := os.Open(p.checkDir)
 	if err != nil {
 		return "", errors.WithStack(err)
diff --git a/lite/files/provider_test.go b/lite/files/provider_test.go
index 23743bfc..7faf7c5e 100644
--- a/lite/files/provider_test.go
+++ b/lite/files/provider_test.go
@@ -45,7 +45,7 @@ func TestFileProvider(t *testing.T) {
 		// two seeds for each validator, to check how we handle dups
 		// (10, 0), (10, 1), (10, 1), (10, 2), (10, 2), ...
 		vals := keys.ToValidators(10, int64(count/2))
-		h := 20 + 10*i
+		h := uint64(20 + 10*i)
 		check := keys.GenCommit(chainID, h, nil, vals, appHash, 0, 5)
 		seeds[i] = lite.NewFullCommit(check, vals)
 	}
@@ -86,7 +86,7 @@ func TestFileProvider(t *testing.T) {
 	seed, err = p.GetByHeight(47)
 	if assert.Nil(err, "%+v", err) {
 		// we only step by 10, so 40 must be the one below this
-		assert.Equal(40, seed.Height())
+		assert.EqualValues(40, seed.Height())
 	}
 
 	// and proper error for too low
diff --git a/lite/helpers.go b/lite/helpers.go
index e68460be..e12f087f 100644
--- a/lite/helpers.go
+++ b/lite/helpers.go
@@ -108,7 +108,7 @@ func makeVote(header *types.Header, vals *types.ValidatorSet, key crypto.PrivKey
 
 // Silences warning that vals can also be merkle.Hashable
 // nolint: interfacer
-func genHeader(chainID string, height int, txs types.Txs,
+func genHeader(chainID string, height uint64, txs types.Txs,
 	vals *types.ValidatorSet, appHash []byte) *types.Header {
 
 	return &types.Header{
@@ -125,7 +125,7 @@ func genHeader(chainID string, height int, txs types.Txs,
 }
 
 // GenCommit calls genHeader and signHeader and combines them into a Commit.
-func (v ValKeys) GenCommit(chainID string, height int, txs types.Txs,
+func (v ValKeys) GenCommit(chainID string, height uint64, txs types.Txs,
 	vals *types.ValidatorSet, appHash []byte, first, last int) Commit {
 
 	header := genHeader(chainID, height, txs, vals, appHash)
@@ -137,7 +137,7 @@ func (v ValKeys) GenCommit(chainID string, height int, txs types.Txs,
 }
 
 // GenFullCommit calls genHeader and signHeader and combines them into a Commit.
-func (v ValKeys) GenFullCommit(chainID string, height int, txs types.Txs,
+func (v ValKeys) GenFullCommit(chainID string, height uint64, txs types.Txs,
 	vals *types.ValidatorSet, appHash []byte, first, last int) FullCommit {
 
 	header := genHeader(chainID, height, txs, vals, appHash)
diff --git a/lite/inquirer.go b/lite/inquirer.go
index 39aa62b3..4c2655f6 100644
--- a/lite/inquirer.go
+++ b/lite/inquirer.go
@@ -46,7 +46,7 @@ func (c *Inquiring) Validators() *types.ValidatorSet {
 }
 
 // LastHeight returns the last height.
-func (c *Inquiring) LastHeight() int {
+func (c *Inquiring) LastHeight() uint64 {
 	return c.cert.lastHeight
 }
 
@@ -95,7 +95,7 @@ func (c *Inquiring) Update(fc FullCommit) error {
 	return err
 }
 
-func (c *Inquiring) useClosestTrust(h int) error {
+func (c *Inquiring) useClosestTrust(h uint64) error {
 	closest, err := c.trusted.GetByHeight(h)
 	if err != nil {
 		return err
@@ -126,7 +126,7 @@ func (c *Inquiring) updateToHash(vhash []byte) error {
 }
 
 // updateToHeight will use divide-and-conquer to find a path to h
-func (c *Inquiring) updateToHeight(h int) error {
+func (c *Inquiring) updateToHeight(h uint64) error {
 	// try to update to this height (with checks)
 	fc, err := c.Source.GetByHeight(h)
 	if err != nil {
diff --git a/lite/inquirer_test.go b/lite/inquirer_test.go
index 82c97f0a..4e315e14 100644
--- a/lite/inquirer_test.go
+++ b/lite/inquirer_test.go
@@ -28,7 +28,7 @@ func TestInquirerValidPath(t *testing.T) {
 		// extend the keys by 1 each time
 		keys = keys.Extend(1)
 		vals := keys.ToValidators(vote, 0)
-		h := 20 + 10*i
+		h := uint64(20 + 10*i)
 		appHash := []byte(fmt.Sprintf("h=%d", h))
 		commits[i] = keys.GenFullCommit(chainID, h, nil, vals, appHash, 0, len(keys))
 	}
@@ -75,7 +75,7 @@ func TestInquirerMinimalPath(t *testing.T) {
 		// extend the validators, so we are just below 2/3
 		keys = keys.Extend(len(keys)/2 - 1)
 		vals := keys.ToValidators(vote, 0)
-		h := 5 + 10*i
+		h := uint64(5 + 10*i)
 		appHash := []byte(fmt.Sprintf("h=%d", h))
 		commits[i] = keys.GenFullCommit(chainID, h, nil, vals, appHash, 0, len(keys))
 	}
@@ -122,7 +122,7 @@ func TestInquirerVerifyHistorical(t *testing.T) {
 		// extend the keys by 1 each time
 		keys = keys.Extend(1)
 		vals := keys.ToValidators(vote, 0)
-		h := 20 + 10*i
+		h := uint64(20 + 10*i)
 		appHash := []byte(fmt.Sprintf("h=%d", h))
 		commits[i] = keys.GenFullCommit(chainID, h, nil, vals, appHash, 0, len(keys))
 	}
diff --git a/lite/memprovider.go b/lite/memprovider.go
index ead043e9..03c99630 100644
--- a/lite/memprovider.go
+++ b/lite/memprovider.go
@@ -52,7 +52,7 @@ func (m *memStoreProvider) StoreCommit(fc FullCommit) error {
 }
 
 // GetByHeight returns the FullCommit for height h or an error if the commit is not found.
-func (m *memStoreProvider) GetByHeight(h int) (FullCommit, error) {
+func (m *memStoreProvider) GetByHeight(h uint64) (FullCommit, error) {
 	// search from highest to lowest
 	for i := len(m.byHeight) - 1; i >= 0; i-- {
 		fc := m.byHeight[i]
diff --git a/lite/performance_test.go b/lite/performance_test.go
index fe4b927a..da571d0e 100644
--- a/lite/performance_test.go
+++ b/lite/performance_test.go
@@ -31,7 +31,7 @@ func benchmarkGenCommit(b *testing.B, keys lite.ValKeys) {
 	chainID := fmt.Sprintf("bench-%d", len(keys))
 	vals := keys.ToValidators(20, 10)
 	for i := 0; i < b.N; i++ {
-		h := 1 + i
+		h := uint64(1 + i)
 		appHash := []byte(fmt.Sprintf("h=%d", h))
 		keys.GenCommit(chainID, h, nil, vals, appHash, 0, len(keys))
 	}
diff --git a/lite/provider.go b/lite/provider.go
index 0084fb35..d3364ff1 100644
--- a/lite/provider.go
+++ b/lite/provider.go
@@ -9,7 +9,7 @@ type Provider interface {
 	// store of trusted commits.
 	StoreCommit(fc FullCommit) error
 	// GetByHeight returns the closest commit with height <= h.
-	GetByHeight(h int) (FullCommit, error)
+	GetByHeight(h uint64) (FullCommit, error)
 	// GetByHash returns a commit exactly matching this validator hash.
 	GetByHash(hash []byte) (FullCommit, error)
 	// LatestCommit returns the newest commit stored.
@@ -55,7 +55,7 @@ func (c cacheProvider) StoreCommit(fc FullCommit) (err error) {
 // Thus, we query each provider in order until we find an exact match
 // or we finished querying them all.  If at least one returned a non-error,
 // then this returns the best match (minimum h-h').
-func (c cacheProvider) GetByHeight(h int) (fc FullCommit, err error) {
+func (c cacheProvider) GetByHeight(h uint64) (fc FullCommit, err error) {
 	for _, p := range c.Providers {
 		var tfc FullCommit
 		tfc, err = p.GetByHeight(h)
diff --git a/lite/provider_test.go b/lite/provider_test.go
index 67754a69..9b8ac15f 100644
--- a/lite/provider_test.go
+++ b/lite/provider_test.go
@@ -21,7 +21,7 @@ func NewMissingProvider() lite.Provider {
 }
 
 func (missingProvider) StoreCommit(lite.FullCommit) error { return nil }
-func (missingProvider) GetByHeight(int) (lite.FullCommit, error) {
+func (missingProvider) GetByHeight(uint64) (lite.FullCommit, error) {
 	return lite.FullCommit{}, liteErr.ErrCommitNotFound()
 }
 func (missingProvider) GetByHash([]byte) (lite.FullCommit, error) {
@@ -57,7 +57,7 @@ func checkProvider(t *testing.T, p lite.Provider, chainID, app string) {
 		// two commits for each validator, to check how we handle dups
 		// (10, 0), (10, 1), (10, 1), (10, 2), (10, 2), ...
 		vals := keys.ToValidators(10, int64(count/2))
-		h := 20 + 10*i
+		h := uint64(20 + 10*i)
 		commits[i] = keys.GenFullCommit(chainID, h, nil, vals, appHash, 0, 5)
 	}
 
@@ -95,13 +95,13 @@ func checkProvider(t *testing.T, p lite.Provider, chainID, app string) {
 	fc, err = p.GetByHeight(47)
 	if assert.Nil(err) {
 		// we only step by 10, so 40 must be the one below this
-		assert.Equal(40, fc.Height())
+		assert.EqualValues(40, fc.Height())
 	}
 
 }
 
 // this will make a get height, and if it is good, set the data as well
-func checkGetHeight(t *testing.T, p lite.Provider, ask, expect int) {
+func checkGetHeight(t *testing.T, p lite.Provider, ask, expect uint64) {
 	fc, err := p.GetByHeight(ask)
 	require.Nil(t, err, "%+v", err)
 	if assert.Equal(t, expect, fc.Height()) {
@@ -128,7 +128,7 @@ func TestCacheGetsBestHeight(t *testing.T) {
 	// set a bunch of commits
 	for i := 0; i < count; i++ {
 		vals := keys.ToValidators(10, int64(count/2))
-		h := 10 * (i + 1)
+		h := uint64(10 * (i + 1))
 		fc := keys.GenFullCommit(chainID, h, nil, vals, appHash, 0, 5)
 		err := p2.StoreCommit(fc)
 		require.NoError(err)
diff --git a/lite/static_test.go b/lite/static_test.go
index c043dea8..4ee7cc03 100644
--- a/lite/static_test.go
+++ b/lite/static_test.go
@@ -26,7 +26,7 @@ func TestStaticCert(t *testing.T) {
 	cases := []struct {
 		keys        lite.ValKeys
 		vals        *types.ValidatorSet
-		height      int
+		height      uint64
 		first, last int  // who actually signs
 		proper      bool // true -> expect no error
 		changed     bool // true -> expect validator change error
diff --git a/mempool/mempool.go b/mempool/mempool.go
index 7ccea410..3bf946be 100644
--- a/mempool/mempool.go
+++ b/mempool/mempool.go
@@ -61,12 +61,12 @@ type Mempool struct {
 	proxyAppConn         proxy.AppConnMempool
 	txs                  *clist.CList    // concurrent linked-list of good txs
 	counter              int64           // simple incrementing counter
-	height               int             // the last block Update()'d to
+	height               uint64          // the last block Update()'d to
 	rechecking           int32           // for re-checking filtered txs on Update()
 	recheckCursor        *clist.CElement // next expected response
 	recheckEnd           *clist.CElement // re-checking stops here
 	notifiedTxsAvailable bool            // true if fired on txsAvailable for this height
-	txsAvailable         chan int        // fires the next height once for each height, when the mempool is not empty
+	txsAvailable         chan uint64        // fires the next height once for each height, when the mempool is not empty
 
 	// Keep a cache of already-seen txs.
 	// This reduces the pressure on the proxyApp.
@@ -80,7 +80,7 @@ type Mempool struct {
 
 // NewMempool returns a new Mempool with the given configuration and connection to an application.
 // TODO: Extract logger into arguments.
-func NewMempool(config *cfg.MempoolConfig, proxyAppConn proxy.AppConnMempool, height int) *Mempool {
+func NewMempool(config *cfg.MempoolConfig, proxyAppConn proxy.AppConnMempool, height uint64) *Mempool {
 	mempool := &Mempool{
 		config:        config,
 		proxyAppConn:  proxyAppConn,
@@ -102,7 +102,7 @@ func NewMempool(config *cfg.MempoolConfig, proxyAppConn proxy.AppConnMempool, he
 // ensuring it will trigger once every height when transactions are available.
 // NOTE: not thread safe - should only be called once, on startup
 func (mem *Mempool) EnableTxsAvailable() {
-	mem.txsAvailable = make(chan int, 1)
+	mem.txsAvailable = make(chan uint64, 1)
 }
 
 // SetLogger sets the Logger.
@@ -249,7 +249,7 @@ func (mem *Mempool) resCbNormal(req *abci.Request, res *abci.Response) {
 			mem.counter++
 			memTx := &mempoolTx{
 				counter: mem.counter,
-				height:  int64(mem.height),
+				height:  mem.height,
 				tx:      tx,
 			}
 			mem.txs.PushBack(memTx)
@@ -310,7 +310,7 @@ func (mem *Mempool) resCbRecheck(req *abci.Request, res *abci.Response) {
 // TxsAvailable returns a channel which fires once for every height,
 // and only when transactions are available in the mempool.
 // NOTE: the returned channel may be nil if EnableTxsAvailable was not called.
-func (mem *Mempool) TxsAvailable() <-chan int {
+func (mem *Mempool) TxsAvailable() <-chan uint64 {
 	return mem.txsAvailable
 }
 
@@ -357,7 +357,7 @@ func (mem *Mempool) collectTxs(maxTxs int) types.Txs {
 // Update informs the mempool that the given txs were committed and can be discarded.
 // NOTE: this should be called *after* block is committed by consensus.
 // NOTE: unsafe; Lock/Unlock must be managed by caller
-func (mem *Mempool) Update(height int, txs types.Txs) error {
+func (mem *Mempool) Update(height uint64, txs types.Txs) error {
 	if err := mem.proxyAppConn.FlushSync(); err != nil { // To flush async resCb calls e.g. from CheckTx
 		return err
 	}
@@ -427,13 +427,13 @@ func (mem *Mempool) recheckTxs(goodTxs []types.Tx) {
 // mempoolTx is a transaction that successfully ran
 type mempoolTx struct {
 	counter int64    // a simple incrementing counter
-	height  int64    // height that this tx had been validated in
+	height  uint64   // height that this tx had been validated in
 	tx      types.Tx //
 }
 
 // Height returns the height for this transaction
-func (memTx *mempoolTx) Height() int {
-	return int(atomic.LoadInt64(&memTx.height))
+func (memTx *mempoolTx) Height() uint64 {
+	return uint64(atomic.LoadUint64(&memTx.height))
 }
 
 //--------------------------------------------------------------------------------
diff --git a/mempool/mempool_test.go b/mempool/mempool_test.go
index e26ef966..4db76107 100644
--- a/mempool/mempool_test.go
+++ b/mempool/mempool_test.go
@@ -37,7 +37,7 @@ func newMempoolWithApp(cc proxy.ClientCreator) *Mempool {
 	return mempool
 }
 
-func ensureNoFire(t *testing.T, ch <-chan int, timeoutMS int) {
+func ensureNoFire(t *testing.T, ch <-chan uint64, timeoutMS int) {
 	timer := time.NewTimer(time.Duration(timeoutMS) * time.Millisecond)
 	select {
 	case <-ch:
@@ -46,7 +46,7 @@ func ensureNoFire(t *testing.T, ch <-chan int, timeoutMS int) {
 	}
 }
 
-func ensureFire(t *testing.T, ch <-chan int, timeoutMS int) {
+func ensureFire(t *testing.T, ch <-chan uint64, timeoutMS int) {
 	timer := time.NewTimer(time.Duration(timeoutMS) * time.Millisecond)
 	select {
 	case <-ch:
diff --git a/mempool/reactor.go b/mempool/reactor.go
index 9e51d2df..d22ffcda 100644
--- a/mempool/reactor.go
+++ b/mempool/reactor.go
@@ -97,7 +97,7 @@ func (memR *MempoolReactor) BroadcastTx(tx types.Tx, cb func(*abci.Response)) er
 
 // PeerState describes the state of a peer.
 type PeerState interface {
-	GetHeight() int
+	GetHeight() uint64
 }
 
 // Peer describes a peer.
diff --git a/rpc/client/event_test.go b/rpc/client/event_test.go
index 96328229..44a1410d 100644
--- a/rpc/client/event_test.go
+++ b/rpc/client/event_test.go
@@ -53,7 +53,7 @@ func TestBlockEvents(t *testing.T) {
 		}
 
 		// listen for a new block; ensure height increases by 1
-		var firstBlockHeight int
+		var firstBlockHeight uint64
 		for j := 0; j < 3; j++ {
 			evtTyp := types.EventNewBlock
 			evt, err := client.WaitForOneEvent(c, evtTyp, waitForEventTimeout)
@@ -67,7 +67,7 @@ func TestBlockEvents(t *testing.T) {
 				continue
 			}
 
-			require.Equal(block.Header.Height, firstBlockHeight+j)
+			require.Equal(block.Header.Height, firstBlockHeight+uint64(j))
 		}
 	}
 }
diff --git a/rpc/client/helpers.go b/rpc/client/helpers.go
index c2f06c00..c2925393 100644
--- a/rpc/client/helpers.go
+++ b/rpc/client/helpers.go
@@ -32,7 +32,7 @@ func DefaultWaitStrategy(delta int) (abort error) {
 //
 // If waiter is nil, we use DefaultWaitStrategy, but you can also
 // provide your own implementation
-func WaitForHeight(c StatusClient, h int, waiter Waiter) error {
+func WaitForHeight(c StatusClient, h uint64, waiter Waiter) error {
 	if waiter == nil {
 		waiter = DefaultWaitStrategy
 	}
@@ -42,7 +42,7 @@ func WaitForHeight(c StatusClient, h int, waiter Waiter) error {
 		if err != nil {
 			return err
 		}
-		delta = h - s.LatestBlockHeight
+		delta = int(h - s.LatestBlockHeight)
 		// wait for the time, or abort early
 		if err := waiter(delta); err != nil {
 			return err
diff --git a/rpc/client/helpers_test.go b/rpc/client/helpers_test.go
index fe186122..ca0884e6 100644
--- a/rpc/client/helpers_test.go
+++ b/rpc/client/helpers_test.go
@@ -66,11 +66,11 @@ func TestWaitForHeight(t *testing.T) {
 	require.Nil(pre.Error)
 	prer, ok := pre.Response.(*ctypes.ResultStatus)
 	require.True(ok)
-	assert.Equal(10, prer.LatestBlockHeight)
+	assert.Equal(uint64(10), prer.LatestBlockHeight)
 
 	post := r.Calls[4]
 	require.Nil(post.Error)
 	postr, ok := post.Response.(*ctypes.ResultStatus)
 	require.True(ok)
-	assert.Equal(15, postr.LatestBlockHeight)
+	assert.Equal(uint64(15), postr.LatestBlockHeight)
 }
diff --git a/rpc/client/httpclient.go b/rpc/client/httpclient.go
index 5ceace97..9fcaec54 100644
--- a/rpc/client/httpclient.go
+++ b/rpc/client/httpclient.go
@@ -123,7 +123,7 @@ func (c *HTTP) DumpConsensusState() (*ctypes.ResultDumpConsensusState, error) {
 	return result, nil
 }
 
-func (c *HTTP) BlockchainInfo(minHeight, maxHeight int) (*ctypes.ResultBlockchainInfo, error) {
+func (c *HTTP) BlockchainInfo(minHeight, maxHeight uint64) (*ctypes.ResultBlockchainInfo, error) {
 	result := new(ctypes.ResultBlockchainInfo)
 	_, err := c.rpc.Call("blockchain",
 		map[string]interface{}{"minHeight": minHeight, "maxHeight": maxHeight},
@@ -143,7 +143,7 @@ func (c *HTTP) Genesis() (*ctypes.ResultGenesis, error) {
 	return result, nil
 }
 
-func (c *HTTP) Block(height *int) (*ctypes.ResultBlock, error) {
+func (c *HTTP) Block(height *uint64) (*ctypes.ResultBlock, error) {
 	result := new(ctypes.ResultBlock)
 	_, err := c.rpc.Call("block", map[string]interface{}{"height": height}, result)
 	if err != nil {
@@ -152,7 +152,7 @@ func (c *HTTP) Block(height *int) (*ctypes.ResultBlock, error) {
 	return result, nil
 }
 
-func (c *HTTP) Commit(height *int) (*ctypes.ResultCommit, error) {
+func (c *HTTP) Commit(height *uint64) (*ctypes.ResultCommit, error) {
 	result := new(ctypes.ResultCommit)
 	_, err := c.rpc.Call("commit", map[string]interface{}{"height": height}, result)
 	if err != nil {
@@ -187,7 +187,7 @@ func (c *HTTP) TxSearch(query string, prove bool) ([]*ctypes.ResultTx, error) {
 	return *results, nil
 }
 
-func (c *HTTP) Validators(height *int) (*ctypes.ResultValidators, error) {
+func (c *HTTP) Validators(height *uint64) (*ctypes.ResultValidators, error) {
 	result := new(ctypes.ResultValidators)
 	_, err := c.rpc.Call("validators", map[string]interface{}{"height": height}, result)
 	if err != nil {
diff --git a/rpc/client/interface.go b/rpc/client/interface.go
index c0d7e052..b154312c 100644
--- a/rpc/client/interface.go
+++ b/rpc/client/interface.go
@@ -46,9 +46,9 @@ type ABCIClient interface {
 // SignClient groups together the interfaces need to get valid
 // signatures and prove anything about the chain
 type SignClient interface {
-	Block(height *int) (*ctypes.ResultBlock, error)
-	Commit(height *int) (*ctypes.ResultCommit, error)
-	Validators(height *int) (*ctypes.ResultValidators, error)
+	Block(height *uint64) (*ctypes.ResultBlock, error)
+	Commit(height *uint64) (*ctypes.ResultCommit, error)
+	Validators(height *uint64) (*ctypes.ResultValidators, error)
 	Tx(hash []byte, prove bool) (*ctypes.ResultTx, error)
 	TxSearch(query string, prove bool) ([]*ctypes.ResultTx, error)
 }
@@ -56,7 +56,7 @@ type SignClient interface {
 // HistoryClient shows us data from genesis to now in large chunks.
 type HistoryClient interface {
 	Genesis() (*ctypes.ResultGenesis, error)
-	BlockchainInfo(minHeight, maxHeight int) (*ctypes.ResultBlockchainInfo, error)
+	BlockchainInfo(minHeight, maxHeight uint64) (*ctypes.ResultBlockchainInfo, error)
 }
 
 type StatusClient interface {
diff --git a/rpc/client/localclient.go b/rpc/client/localclient.go
index d5444007..123d82f8 100644
--- a/rpc/client/localclient.go
+++ b/rpc/client/localclient.go
@@ -100,7 +100,7 @@ func (Local) DialSeeds(seeds []string) (*ctypes.ResultDialSeeds, error) {
 	return core.UnsafeDialSeeds(seeds)
 }
 
-func (Local) BlockchainInfo(minHeight, maxHeight int) (*ctypes.ResultBlockchainInfo, error) {
+func (Local) BlockchainInfo(minHeight, maxHeight uint64) (*ctypes.ResultBlockchainInfo, error) {
 	return core.BlockchainInfo(minHeight, maxHeight)
 }
 
@@ -108,15 +108,15 @@ func (Local) Genesis() (*ctypes.ResultGenesis, error) {
 	return core.Genesis()
 }
 
-func (Local) Block(height *int) (*ctypes.ResultBlock, error) {
+func (Local) Block(height *uint64) (*ctypes.ResultBlock, error) {
 	return core.Block(height)
 }
 
-func (Local) Commit(height *int) (*ctypes.ResultCommit, error) {
+func (Local) Commit(height *uint64) (*ctypes.ResultCommit, error) {
 	return core.Commit(height)
 }
 
-func (Local) Validators(height *int) (*ctypes.ResultValidators, error) {
+func (Local) Validators(height *uint64) (*ctypes.ResultValidators, error) {
 	return core.Validators(height)
 }
 
diff --git a/rpc/client/mock/client.go b/rpc/client/mock/client.go
index 7fc45206..9eb0150c 100644
--- a/rpc/client/mock/client.go
+++ b/rpc/client/mock/client.go
@@ -111,7 +111,7 @@ func (c Client) DialSeeds(seeds []string) (*ctypes.ResultDialSeeds, error) {
 	return core.UnsafeDialSeeds(seeds)
 }
 
-func (c Client) BlockchainInfo(minHeight, maxHeight int) (*ctypes.ResultBlockchainInfo, error) {
+func (c Client) BlockchainInfo(minHeight, maxHeight uint64) (*ctypes.ResultBlockchainInfo, error) {
 	return core.BlockchainInfo(minHeight, maxHeight)
 }
 
@@ -119,14 +119,14 @@ func (c Client) Genesis() (*ctypes.ResultGenesis, error) {
 	return core.Genesis()
 }
 
-func (c Client) Block(height *int) (*ctypes.ResultBlock, error) {
+func (c Client) Block(height *uint64) (*ctypes.ResultBlock, error) {
 	return core.Block(height)
 }
 
-func (c Client) Commit(height *int) (*ctypes.ResultCommit, error) {
+func (c Client) Commit(height *uint64) (*ctypes.ResultCommit, error) {
 	return core.Commit(height)
 }
 
-func (c Client) Validators(height *int) (*ctypes.ResultValidators, error) {
+func (c Client) Validators(height *uint64) (*ctypes.ResultValidators, error) {
 	return core.Validators(height)
 }
diff --git a/rpc/core/blocks.go b/rpc/core/blocks.go
index 6b5e2166..0b785828 100644
--- a/rpc/core/blocks.go
+++ b/rpc/core/blocks.go
@@ -61,16 +61,16 @@ import (
 // ```
 //
 // <aside class="notice">Returns at most 20 items.</aside>
-func BlockchainInfo(minHeight, maxHeight int) (*ctypes.ResultBlockchainInfo, error) {
+func BlockchainInfo(minHeight, maxHeight uint64) (*ctypes.ResultBlockchainInfo, error) {
 	if maxHeight == 0 {
 		maxHeight = blockStore.Height()
 	} else {
-		maxHeight = cmn.MinInt(blockStore.Height(), maxHeight)
+		maxHeight = cmn.MinUint64(blockStore.Height(), maxHeight)
 	}
 	if minHeight == 0 {
-		minHeight = cmn.MaxInt(1, maxHeight-20)
+		minHeight = cmn.MaxUint64(1, maxHeight-20)
 	} else {
-		minHeight = cmn.MaxInt(minHeight, maxHeight-20)
+		minHeight = cmn.MaxUint64(minHeight, maxHeight-20)
 	}
 
 	logger.Debug("BlockchainInfoHandler", "maxHeight", maxHeight, "minHeight", minHeight)
@@ -184,7 +184,7 @@ func BlockchainInfo(minHeight, maxHeight int) (*ctypes.ResultBlockchainInfo, err
 //   "jsonrpc": "2.0"
 // }
 // ```
-func Block(heightPtr *int) (*ctypes.ResultBlock, error) {
+func Block(heightPtr *uint64) (*ctypes.ResultBlock, error) {
 	if heightPtr == nil {
 		height := blockStore.Height()
 		blockMeta := blockStore.LoadBlockMeta(height)
@@ -275,7 +275,7 @@ func Block(heightPtr *int) (*ctypes.ResultBlock, error) {
 //   "jsonrpc": "2.0"
 // }
 // ```
-func Commit(heightPtr *int) (*ctypes.ResultCommit, error) {
+func Commit(heightPtr *uint64) (*ctypes.ResultCommit, error) {
 	if heightPtr == nil {
 		height := blockStore.Height()
 		header := blockStore.LoadBlockMeta(height).Header
diff --git a/rpc/core/consensus.go b/rpc/core/consensus.go
index 75ce08a9..11767d5e 100644
--- a/rpc/core/consensus.go
+++ b/rpc/core/consensus.go
@@ -42,7 +42,7 @@ import (
 // 	"jsonrpc": "2.0"
 // }
 // ```
-func Validators(heightPtr *int) (*ctypes.ResultValidators, error) {
+func Validators(heightPtr *uint64) (*ctypes.ResultValidators, error) {
 	if heightPtr == nil {
 		blockHeight, validators := consensusState.GetValidators()
 		return &ctypes.ResultValidators{blockHeight, validators}, nil
diff --git a/rpc/core/pipe.go b/rpc/core/pipe.go
index 0f3f7472..ae89da8b 100644
--- a/rpc/core/pipe.go
+++ b/rpc/core/pipe.go
@@ -21,7 +21,7 @@ var subscribeTimeout = 5 * time.Second
 
 type Consensus interface {
 	GetState() *sm.State
-	GetValidators() (int, []*types.Validator)
+	GetValidators() (uint64, []*types.Validator)
 	GetRoundState() *cstypes.RoundState
 }
 
diff --git a/rpc/core/tx.go b/rpc/core/tx.go
index b6973591..3ebb0d11 100644
--- a/rpc/core/tx.go
+++ b/rpc/core/tx.go
@@ -84,7 +84,7 @@ func Tx(hash []byte, prove bool) (*ctypes.ResultTx, error) {
 	}
 
 	height := r.Height
-	index := r.Index
+	index := int(r.Index) // XXX:overflow
 
 	var proof types.TxProof
 	if prove {
diff --git a/rpc/core/types/responses.go b/rpc/core/types/responses.go
index a1b7e36f..983d1383 100644
--- a/rpc/core/types/responses.go
+++ b/rpc/core/types/responses.go
@@ -12,7 +12,7 @@ import (
 )
 
 type ResultBlockchainInfo struct {
-	LastHeight int                `json:"last_height"`
+	LastHeight uint64             `json:"last_height"`
 	BlockMetas []*types.BlockMeta `json:"block_metas"`
 }
 
@@ -51,7 +51,7 @@ type ResultStatus struct {
 	PubKey            crypto.PubKey `json:"pub_key"`
 	LatestBlockHash   data.Bytes    `json:"latest_block_hash"`
 	LatestAppHash     data.Bytes    `json:"latest_app_hash"`
-	LatestBlockHeight int           `json:"latest_block_height"`
+	LatestBlockHeight uint64        `json:"latest_block_height"`
 	LatestBlockTime   int64         `json:"latest_block_time"` // nano
 	Syncing           bool          `json:"syncing"`
 }
@@ -86,7 +86,7 @@ type Peer struct {
 }
 
 type ResultValidators struct {
-	BlockHeight int                `json:"block_height"`
+	BlockHeight uint64             `json:"block_height"`
 	Validators  []*types.Validator `json:"validators"`
 }
 
diff --git a/state/errors.go b/state/errors.go
index 4a87384a..16f1a4e6 100644
--- a/state/errors.go
+++ b/state/errors.go
@@ -9,22 +9,22 @@ type (
 	ErrProxyAppConn error
 
 	ErrUnknownBlock struct {
-		Height int
+		Height uint64
 	}
 
 	ErrBlockHashMismatch struct {
 		CoreHash []byte
 		AppHash  []byte
-		Height   int
+		Height   uint64
 	}
 
 	ErrAppBlockHeightTooHigh struct {
-		CoreHeight int
-		AppHeight  int
+		CoreHeight uint64
+		AppHeight  uint64
 	}
 
 	ErrLastStateMismatch struct {
-		Height int
+		Height uint64
 		Core   []byte
 		App    []byte
 	}
@@ -35,7 +35,7 @@ type (
 	}
 
 	ErrNoValSetForHeight struct {
-		Height int
+		Height uint64
 	}
 )
 
diff --git a/state/execution.go b/state/execution.go
index 3622a663..42d940db 100644
--- a/state/execution.go
+++ b/state/execution.go
@@ -8,6 +8,7 @@ import (
 	abci "github.com/tendermint/abci/types"
 	crypto "github.com/tendermint/go-crypto"
 	"github.com/tendermint/tendermint/proxy"
+	"github.com/tendermint/tendermint/state/txindex"
 	"github.com/tendermint/tendermint/types"
 	cmn "github.com/tendermint/tmlibs/common"
 	"github.com/tendermint/tmlibs/log"
@@ -270,6 +271,26 @@ func (s *State) CommitStateUpdateMempool(proxyAppConn proxy.AppConnConsensus, bl
 	return mempool.Update(block.Height, block.Txs)
 }
 
+func (s *State) indexTxs(abciResponses *ABCIResponses) {
+	// save the tx results using the TxIndexer
+	// NOTE: these may be overwriting, but the values should be the same.
+	batch := txindex.NewBatch(len(abciResponses.DeliverTx))
+	for i, d := range abciResponses.DeliverTx {
+		tx := abciResponses.txs[i]
+		if err := batch.Add(types.TxResult{
+			Height: abciResponses.Height,
+			Index:  uint32(i),
+			Tx:     tx,
+			Result: *d,
+		}); err != nil {
+			s.logger.Error("Error with batch.Add", "err", err)
+		}
+	}
+	if err := s.TxIndexer.AddBatch(batch); err != nil {
+		s.logger.Error("Error adding batch", "err", err)
+	}
+}
+
 // ExecCommitBlock executes and commits a block on the proxyApp without validating or mutating the state.
 // It returns the application root hash (result of abci.Commit).
 func ExecCommitBlock(appConnConsensus proxy.AppConnConsensus, block *types.Block, logger log.Logger) ([]byte, error) {
diff --git a/state/execution_test.go b/state/execution_test.go
index e54d983d..bb239fe4 100644
--- a/state/execution_test.go
+++ b/state/execution_test.go
@@ -43,9 +43,9 @@ func TestApplyBlock(t *testing.T) {
 //----------------------------------------------------------------------------
 
 // make some bogus txs
-func makeTxs(blockNum int) (txs []types.Tx) {
+func makeTxs(height uint64) (txs []types.Tx) {
 	for i := 0; i < nTxsPerBlock; i++ {
-		txs = append(txs, types.Tx([]byte{byte(blockNum), byte(i)}))
+		txs = append(txs, types.Tx([]byte{byte(height), byte(i)}))
 	}
 	return txs
 }
@@ -61,12 +61,12 @@ func state() *State {
 	return s
 }
 
-func makeBlock(num int, state *State) *types.Block {
+func makeBlock(height uint64, state *State) *types.Block {
 	prevHash := state.LastBlockID.Hash
 	prevParts := types.PartSetHeader{}
 	valHash := state.Validators.Hash()
 	prevBlockID := types.BlockID{prevHash, prevParts}
-	block, _ := types.MakeBlock(num, chainID, makeTxs(num), new(types.Commit),
+	block, _ := types.MakeBlock(height, chainID, makeTxs(height), new(types.Commit),
 		prevBlockID, valHash, state.AppHash, testPartSize)
 	return block
 }
diff --git a/state/state.go b/state/state.go
index e1f16835..aa2566f0 100644
--- a/state/state.go
+++ b/state/state.go
@@ -23,7 +23,7 @@ var (
 	abciResponsesKey = []byte("abciResponsesKey")
 )
 
-func calcValidatorsKey(height int) []byte {
+func calcValidatorsKey(height uint64) []byte {
 	return []byte(cmn.Fmt("validatorsKey:%v", height))
 }
 
@@ -45,7 +45,7 @@ type State struct {
 	// These fields are updated by SetBlockAndValidators.
 	// LastBlockHeight=0 at genesis (ie. block(H=0) does not exist)
 	// LastValidators is used to validate block.LastCommit.
-	LastBlockHeight int
+	LastBlockHeight uint64
 	LastBlockID     types.BlockID
 	LastBlockTime   time.Time
 	Validators      *types.ValidatorSet
@@ -54,7 +54,7 @@ type State struct {
 	// the change only applies to the next block.
 	// So, if s.LastBlockHeight causes a valset change,
 	// we set s.LastHeightValidatorsChanged = s.LastBlockHeight + 1
-	LastHeightValidatorsChanged int
+	LastHeightValidatorsChanged uint64
 
 	// AppHash is updated after Commit
 	AppHash []byte
@@ -163,7 +163,7 @@ func (s *State) LoadABCIResponses() *ABCIResponses {
 }
 
 // LoadValidators loads the ValidatorSet for a given height.
-func (s *State) LoadValidators(height int) (*types.ValidatorSet, error) {
+func (s *State) LoadValidators(height uint64) (*types.ValidatorSet, error) {
 	valInfo := s.loadValidators(height)
 	if valInfo == nil {
 		return nil, ErrNoValSetForHeight{height}
@@ -180,7 +180,7 @@ func (s *State) LoadValidators(height int) (*types.ValidatorSet, error) {
 	return valInfo.ValidatorSet, nil
 }
 
-func (s *State) loadValidators(height int) *ValidatorsInfo {
+func (s *State) loadValidators(height uint64) *ValidatorsInfo {
 	buf := s.db.Get(calcValidatorsKey(height))
 	if len(buf) == 0 {
 		return nil
@@ -256,7 +256,7 @@ func (s *State) SetBlockAndValidators(header *types.Header, blockPartsHeader typ
 
 }
 
-func (s *State) setBlockAndValidators(height int, blockID types.BlockID, blockTime time.Time,
+func (s *State) setBlockAndValidators(height uint64, blockID types.BlockID, blockTime time.Time,
 	prevValSet, nextValSet *types.ValidatorSet) {
 
 	s.LastBlockHeight = height
@@ -276,7 +276,7 @@ func (s *State) GetValidators() (last *types.ValidatorSet, current *types.Valida
 // ABCIResponses retains the responses of the various ABCI calls during block processing.
 // It is persisted to disk before calling Commit.
 type ABCIResponses struct {
-	Height int
+	Height uint64
 
 	DeliverTx []*abci.ResponseDeliverTx
 	EndBlock  *abci.ResponseEndBlock
@@ -303,7 +303,7 @@ func (a *ABCIResponses) Bytes() []byte {
 // ValidatorsInfo represents the latest validator set, or the last height it changed
 type ValidatorsInfo struct {
 	ValidatorSet      *types.ValidatorSet
-	LastHeightChanged int
+	LastHeightChanged uint64
 }
 
 // Bytes serializes the ValidatorsInfo using go-wire
diff --git a/state/state_test.go b/state/state_test.go
index 7fff0774..cccfc8b6 100644
--- a/state/state_test.go
+++ b/state/state_test.go
@@ -138,7 +138,7 @@ func TestValidatorChangesSaveLoad(t *testing.T) {
 	assert := assert.New(t)
 
 	// change vals at these heights
-	changeHeights := []int{1, 2, 4, 5, 10, 15, 16, 17, 20}
+	changeHeights := []uint64{1, 2, 4, 5, 10, 15, 16, 17, 20}
 	N := len(changeHeights)
 
 	// each valset is just one validator.
@@ -155,7 +155,7 @@ func TestValidatorChangesSaveLoad(t *testing.T) {
 	highestHeight := changeHeights[N-1] + 5
 	changeIndex := 0
 	pubkey := pubkeys[changeIndex]
-	for i := 1; i < highestHeight; i++ {
+	for i := uint64(1); i < highestHeight; i++ {
 		// when we get to a change height,
 		// use the next pubkey
 		if changeIndex < len(changeHeights) && i == changeHeights[changeIndex] {
@@ -171,7 +171,7 @@ func TestValidatorChangesSaveLoad(t *testing.T) {
 	testCases := make([]valChangeTestCase, highestHeight)
 	changeIndex = 0
 	pubkey = pubkeys[changeIndex]
-	for i := 1; i < highestHeight+1; i++ {
+	for i := uint64(1); i < highestHeight+1; i++ {
 		// we we get to the height after a change height
 		// use the next pubkey (note our counter starts at 0 this time)
 		if changeIndex < len(changeHeights) && i == changeHeights[changeIndex]+1 {
@@ -192,7 +192,7 @@ func TestValidatorChangesSaveLoad(t *testing.T) {
 	}
 }
 
-func makeHeaderPartsResponses(state *State, height int,
+func makeHeaderPartsResponses(state *State, height uint64,
 	pubkey crypto.PubKey) (*types.Header, types.PartSetHeader, *ABCIResponses) {
 
 	block := makeBlock(height, state)
@@ -216,6 +216,6 @@ func makeHeaderPartsResponses(state *State, height int,
 }
 
 type valChangeTestCase struct {
-	height int
+	height uint64
 	vals   crypto.PubKey
 }
diff --git a/types/block.go b/types/block.go
index 738e5a00..eb14fc6c 100644
--- a/types/block.go
+++ b/types/block.go
@@ -23,7 +23,7 @@ type Block struct {
 
 // MakeBlock returns a new block and corresponding partset from the given information.
 // TODO: Add version information to the Block struct.
-func MakeBlock(height int, chainID string, txs []Tx, commit *Commit,
+func MakeBlock(height uint64, chainID string, txs []Tx, commit *Commit,
 	prevBlockID BlockID, valHash, appHash []byte, partSize int) (*Block, *PartSet) {
 	block := &Block{
 		Header: &Header{
@@ -45,7 +45,7 @@ func MakeBlock(height int, chainID string, txs []Tx, commit *Commit,
 }
 
 // ValidateBasic performs basic validation that doesn't involve state data.
-func (b *Block) ValidateBasic(chainID string, lastBlockHeight int, lastBlockID BlockID,
+func (b *Block) ValidateBasic(chainID string, lastBlockHeight uint64, lastBlockID BlockID,
 	lastBlockTime time.Time, appHash []byte) error {
 	if b.ChainID != chainID {
 		return errors.New(cmn.Fmt("Wrong Block.Header.ChainID. Expected %v, got %v", chainID, b.ChainID))
@@ -158,7 +158,7 @@ func (b *Block) StringShort() string {
 // Header defines the structure of a Tendermint block header
 type Header struct {
 	ChainID        string     `json:"chain_id"`
-	Height         int        `json:"height"`
+	Height         uint64     `json:"height"`
 	Time           time.Time  `json:"time"`
 	NumTxs         int        `json:"num_txs"` // XXX: Can we get rid of this?
 	LastBlockID    BlockID    `json:"last_block_id"`
@@ -250,7 +250,7 @@ func (commit *Commit) FirstPrecommit() *Vote {
 }
 
 // Height returns the height of the commit
-func (commit *Commit) Height() int {
+func (commit *Commit) Height() uint64 {
 	if len(commit.Precommits) == 0 {
 		return 0
 	}
diff --git a/types/canonical_json.go b/types/canonical_json.go
index 5f1a0aca..f50c5461 100644
--- a/types/canonical_json.go
+++ b/types/canonical_json.go
@@ -18,7 +18,7 @@ type CanonicalJSONPartSetHeader struct {
 
 type CanonicalJSONProposal struct {
 	BlockPartsHeader CanonicalJSONPartSetHeader `json:"block_parts_header"`
-	Height           int                        `json:"height"`
+	Height           uint64                     `json:"height"`
 	POLBlockID       CanonicalJSONBlockID       `json:"pol_block_id"`
 	POLRound         int                        `json:"pol_round"`
 	Round            int                        `json:"round"`
@@ -26,13 +26,13 @@ type CanonicalJSONProposal struct {
 
 type CanonicalJSONVote struct {
 	BlockID CanonicalJSONBlockID `json:"block_id"`
-	Height  int                  `json:"height"`
+	Height  uint64               `json:"height"`
 	Round   int                  `json:"round"`
 	Type    byte                 `json:"type"`
 }
 
 type CanonicalJSONHeartbeat struct {
-	Height           int        `json:"height"`
+	Height           uint64     `json:"height"`
 	Round            int        `json:"round"`
 	Sequence         int        `json:"sequence"`
 	ValidatorAddress data.Bytes `json:"validator_address"`
diff --git a/types/events.go b/types/events.go
index 9bf7a5a4..7d161540 100644
--- a/types/events.go
+++ b/types/events.go
@@ -118,7 +118,7 @@ type EventDataProposalHeartbeat struct {
 
 // NOTE: This goes into the replay WAL
 type EventDataRoundState struct {
-	Height int    `json:"height"`
+	Height uint64 `json:"height"`
 	Round  int    `json:"round"`
 	Step   string `json:"step"`
 
diff --git a/types/heartbeat.go b/types/heartbeat.go
index 64676ea6..8d825453 100644
--- a/types/heartbeat.go
+++ b/types/heartbeat.go
@@ -18,7 +18,7 @@ import (
 type Heartbeat struct {
 	ValidatorAddress data.Bytes       `json:"validator_address"`
 	ValidatorIndex   int              `json:"validator_index"`
-	Height           int              `json:"height"`
+	Height           uint64           `json:"height"`
 	Round            int              `json:"round"`
 	Sequence         int              `json:"sequence"`
 	Signature        crypto.Signature `json:"signature"`
diff --git a/types/priv_validator.go b/types/priv_validator.go
index 8834eb7c..493efa26 100644
--- a/types/priv_validator.go
+++ b/types/priv_validator.go
@@ -51,7 +51,7 @@ type PrivValidator interface {
 type PrivValidatorFS struct {
 	Address       data.Bytes       `json:"address"`
 	PubKey        crypto.PubKey    `json:"pub_key"`
-	LastHeight    int              `json:"last_height"`
+	LastHeight    uint64           `json:"last_height"`
 	LastRound     int              `json:"last_round"`
 	LastStep      int8             `json:"last_step"`
 	LastSignature crypto.Signature `json:"last_signature,omitempty"` // so we dont lose signatures
@@ -222,7 +222,7 @@ func (privVal *PrivValidatorFS) SignProposal(chainID string, proposal *Proposal)
 // signBytesHRS signs the given signBytes if the height/round/step (HRS)
 // are greater than the latest state. If the HRS are equal,
 // it returns the privValidator.LastSignature.
-func (privVal *PrivValidatorFS) signBytesHRS(height, round int, step int8, signBytes []byte) (crypto.Signature, error) {
+func (privVal *PrivValidatorFS) signBytesHRS(height uint64, round int, step int8, signBytes []byte) (crypto.Signature, error) {
 
 	sig := crypto.Signature{}
 	// If height regression, err
diff --git a/types/priv_validator_test.go b/types/priv_validator_test.go
index cd2dfc13..4e1636c0 100644
--- a/types/priv_validator_test.go
+++ b/types/priv_validator_test.go
@@ -20,7 +20,7 @@ func TestGenLoadValidator(t *testing.T) {
 	_, tempFilePath := cmn.Tempfile("priv_validator_")
 	privVal := GenPrivValidatorFS(tempFilePath)
 
-	height := 100
+	height := uint64(100)
 	privVal.LastHeight = height
 	privVal.Save()
 	addr := privVal.GetAddress()
@@ -99,7 +99,7 @@ func TestSignVote(t *testing.T) {
 
 	block1 := BlockID{[]byte{1, 2, 3}, PartSetHeader{}}
 	block2 := BlockID{[]byte{3, 2, 1}, PartSetHeader{}}
-	height, round := 10, 1
+	height, round := uint64(10), 1
 	voteType := VoteTypePrevote
 
 	// sign a vote for first time
@@ -133,7 +133,7 @@ func TestSignProposal(t *testing.T) {
 
 	block1 := PartSetHeader{5, []byte{1, 2, 3}}
 	block2 := PartSetHeader{10, []byte{3, 2, 1}}
-	height, round := 10, 1
+	height, round := uint64(10), 1
 
 	// sign a proposal for first time
 	proposal := newProposal(height, round, block1)
@@ -158,7 +158,7 @@ func TestSignProposal(t *testing.T) {
 	}
 }
 
-func newVote(addr data.Bytes, idx, height, round int, typ byte, blockID BlockID) *Vote {
+func newVote(addr data.Bytes, idx int, height uint64, round int, typ byte, blockID BlockID) *Vote {
 	return &Vote{
 		ValidatorAddress: addr,
 		ValidatorIndex:   idx,
@@ -169,7 +169,7 @@ func newVote(addr data.Bytes, idx, height, round int, typ byte, blockID BlockID)
 	}
 }
 
-func newProposal(height, round int, partsHeader PartSetHeader) *Proposal {
+func newProposal(height uint64, round int, partsHeader PartSetHeader) *Proposal {
 	return &Proposal{
 		Height:           height,
 		Round:            round,
diff --git a/types/proposal.go b/types/proposal.go
index 8efa91b6..21e169b5 100644
--- a/types/proposal.go
+++ b/types/proposal.go
@@ -20,7 +20,7 @@ var (
 // to be considered valid. It may depend on votes from a previous round,
 // a so-called Proof-of-Lock (POL) round, as noted in the POLRound and POLBlockID.
 type Proposal struct {
-	Height           int              `json:"height"`
+	Height           uint64           `json:"height"`
 	Round            int              `json:"round"`
 	BlockPartsHeader PartSetHeader    `json:"block_parts_header"`
 	POLRound         int              `json:"pol_round"`    // -1 if null.
@@ -30,7 +30,7 @@ type Proposal struct {
 
 // NewProposal returns a new Proposal.
 // If there is no POLRound, polRound should be -1.
-func NewProposal(height int, round int, blockPartsHeader PartSetHeader, polRound int, polBlockID BlockID) *Proposal {
+func NewProposal(height uint64, round int, blockPartsHeader PartSetHeader, polRound int, polBlockID BlockID) *Proposal {
 	return &Proposal{
 		Height:           height,
 		Round:            round,
diff --git a/types/services.go b/types/services.go
index f025de79..a7d39172 100644
--- a/types/services.go
+++ b/types/services.go
@@ -25,10 +25,10 @@ type Mempool interface {
 	Size() int
 	CheckTx(Tx, func(*abci.Response)) error
 	Reap(int) Txs
-	Update(height int, txs Txs) error
+	Update(height uint64, txs Txs) error
 	Flush()
 
-	TxsAvailable() <-chan int
+	TxsAvailable() <-chan uint64
 	EnableTxsAvailable()
 }
 
@@ -42,9 +42,9 @@ func (m MockMempool) Unlock()                                      {}
 func (m MockMempool) Size() int                                    { return 0 }
 func (m MockMempool) CheckTx(tx Tx, cb func(*abci.Response)) error { return nil }
 func (m MockMempool) Reap(n int) Txs                               { return Txs{} }
-func (m MockMempool) Update(height int, txs Txs) error             { return nil }
+func (m MockMempool) Update(height uint64, txs Txs) error          { return nil }
 func (m MockMempool) Flush()                                       {}
-func (m MockMempool) TxsAvailable() <-chan int                     { return make(chan int) }
+func (m MockMempool) TxsAvailable() <-chan uint64                  { return make(chan uint64) }
 func (m MockMempool) EnableTxsAvailable()                          {}
 
 //------------------------------------------------------
@@ -53,14 +53,14 @@ func (m MockMempool) EnableTxsAvailable()                          {}
 // BlockStoreRPC is the block store interface used by the RPC.
 // UNSTABLE
 type BlockStoreRPC interface {
-	Height() int
+	Height() uint64
 
-	LoadBlockMeta(height int) *BlockMeta
-	LoadBlock(height int) *Block
-	LoadBlockPart(height int, index int) *Part
+	LoadBlockMeta(height uint64) *BlockMeta
+	LoadBlock(height uint64) *Block
+	LoadBlockPart(height uint64, index int) *Part
 
-	LoadBlockCommit(height int) *Commit
-	LoadSeenCommit(height int) *Commit
+	LoadBlockCommit(height uint64) *Commit
+	LoadSeenCommit(height uint64) *Commit
 }
 
 // BlockStore defines the BlockStore interface.
diff --git a/types/validator_set.go b/types/validator_set.go
index 60376a32..97e12ce9 100644
--- a/types/validator_set.go
+++ b/types/validator_set.go
@@ -223,7 +223,7 @@ func (valSet *ValidatorSet) Iterate(fn func(index int, val *Validator) bool) {
 }
 
 // Verify that +2/3 of the set had signed the given signBytes
-func (valSet *ValidatorSet) VerifyCommit(chainID string, blockID BlockID, height int, commit *Commit) error {
+func (valSet *ValidatorSet) VerifyCommit(chainID string, blockID BlockID, height uint64, commit *Commit) error {
 	if valSet.Size() != len(commit.Precommits) {
 		return fmt.Errorf("Invalid commit -- wrong set size: %v vs %v", valSet.Size(), len(commit.Precommits))
 	}
@@ -283,7 +283,7 @@ func (valSet *ValidatorSet) VerifyCommit(chainID string, blockID BlockID, height
 // * 10% of the valset can't just declare themselves kings
 // * If the validator set is 3x old size, we need more proof to trust
 func (valSet *ValidatorSet) VerifyCommitAny(newSet *ValidatorSet, chainID string,
-	blockID BlockID, height int, commit *Commit) error {
+	blockID BlockID, height uint64, commit *Commit) error {
 
 	if newSet.Size() != len(commit.Precommits) {
 		return errors.Errorf("Invalid commit -- wrong set size: %v vs %v", newSet.Size(), len(commit.Precommits))
diff --git a/types/vote.go b/types/vote.go
index d5de6348..544cf67a 100644
--- a/types/vote.go
+++ b/types/vote.go
@@ -51,7 +51,7 @@ func IsVoteTypeValid(type_ byte) bool {
 type Vote struct {
 	ValidatorAddress data.Bytes       `json:"validator_address"`
 	ValidatorIndex   int              `json:"validator_index"`
-	Height           int              `json:"height"`
+	Height           uint64           `json:"height"`
 	Round            int              `json:"round"`
 	Type             byte             `json:"type"`
 	BlockID          BlockID          `json:"block_id"` // zero if vote is nil.
diff --git a/types/vote_set.go b/types/vote_set.go
index 85a839db..579a7e9b 100644
--- a/types/vote_set.go
+++ b/types/vote_set.go
@@ -45,7 +45,7 @@ import (
 */
 type VoteSet struct {
 	chainID string
-	height  int
+	height  uint64
 	round   int
 	type_   byte
 
@@ -60,7 +60,7 @@ type VoteSet struct {
 }
 
 // Constructs a new VoteSet struct used to accumulate votes for given height/round.
-func NewVoteSet(chainID string, height int, round int, type_ byte, valSet *ValidatorSet) *VoteSet {
+func NewVoteSet(chainID string, height uint64, round int, type_ byte, valSet *ValidatorSet) *VoteSet {
 	if height == 0 {
 		cmn.PanicSanity("Cannot make VoteSet for height == 0, doesn't make sense.")
 	}
@@ -83,7 +83,7 @@ func (voteSet *VoteSet) ChainID() string {
 	return voteSet.chainID
 }
 
-func (voteSet *VoteSet) Height() int {
+func (voteSet *VoteSet) Height() uint64 {
 	if voteSet == nil {
 		return 0
 	} else {
@@ -523,7 +523,7 @@ func (vs *blockVotes) getByIndex(index int) *Vote {
 
 // Common interface between *consensus.VoteSet and types.Commit
 type VoteSetReader interface {
-	Height() int
+	Height() uint64
 	Round() int
 	Type() byte
 	Size() int
diff --git a/types/vote_set_test.go b/types/vote_set_test.go
index ebead3ee..713ebbf9 100644
--- a/types/vote_set_test.go
+++ b/types/vote_set_test.go
@@ -4,13 +4,13 @@ import (
 	"bytes"
 	"testing"
 
-	"github.com/tendermint/go-crypto"
+	crypto "github.com/tendermint/go-crypto"
 	cmn "github.com/tendermint/tmlibs/common"
 	tst "github.com/tendermint/tmlibs/test"
 )
 
 // NOTE: privValidators are in order
-func randVoteSet(height int, round int, type_ byte, numValidators int, votingPower int64) (*VoteSet, *ValidatorSet, []*PrivValidatorFS) {
+func randVoteSet(height uint64, round int, type_ byte, numValidators int, votingPower int64) (*VoteSet, *ValidatorSet, []*PrivValidatorFS) {
 	valSet, privValidators := RandValidatorSet(numValidators, votingPower)
 	return NewVoteSet("test_chain_id", height, round, type_, valSet), valSet, privValidators
 }
@@ -24,7 +24,7 @@ func withValidator(vote *Vote, addr []byte, idx int) *Vote {
 }
 
 // Convenience: Return new vote with different height
-func withHeight(vote *Vote, height int) *Vote {
+func withHeight(vote *Vote, height uint64) *Vote {
 	vote = vote.Copy()
 	vote.Height = height
 	return vote
@@ -69,7 +69,7 @@ func signAddVote(privVal *PrivValidatorFS, vote *Vote, voteSet *VoteSet) (bool,
 }
 
 func TestAddVote(t *testing.T) {
-	height, round := 1, 0
+	height, round := uint64(1), 0
 	voteSet, _, privValidators := randVoteSet(height, round, VoteTypePrevote, 10, 1)
 	val0 := privValidators[0]
 
@@ -112,7 +112,7 @@ func TestAddVote(t *testing.T) {
 }
 
 func Test2_3Majority(t *testing.T) {
-	height, round := 1, 0
+	height, round := uint64(1), 0
 	voteSet, _, privValidators := randVoteSet(height, round, VoteTypePrevote, 10, 1)
 
 	voteProto := &Vote{
@@ -164,7 +164,7 @@ func Test2_3Majority(t *testing.T) {
 }
 
 func Test2_3MajorityRedux(t *testing.T) {
-	height, round := 1, 0
+	height, round := uint64(1), 0
 	voteSet, _, privValidators := randVoteSet(height, round, VoteTypePrevote, 100, 1)
 
 	blockHash := crypto.CRandBytes(32)
@@ -262,7 +262,7 @@ func Test2_3MajorityRedux(t *testing.T) {
 }
 
 func TestBadVotes(t *testing.T) {
-	height, round := 1, 0
+	height, round := uint64(1), 0
 	voteSet, _, privValidators := randVoteSet(height, round, VoteTypePrevote, 10, 1)
 
 	voteProto := &Vote{
@@ -321,7 +321,7 @@ func TestBadVotes(t *testing.T) {
 }
 
 func TestConflicts(t *testing.T) {
-	height, round := 1, 0
+	height, round := uint64(1), 0
 	voteSet, _, privValidators := randVoteSet(height, round, VoteTypePrevote, 4, 1)
 	blockHash1 := cmn.RandBytes(32)
 	blockHash2 := cmn.RandBytes(32)
@@ -450,7 +450,7 @@ func TestConflicts(t *testing.T) {
 }
 
 func TestMakeCommit(t *testing.T) {
-	height, round := 1, 0
+	height, round := uint64(1), 0
 	voteSet, _, privValidators := randVoteSet(height, round, VoteTypePrecommit, 10, 1)
 	blockHash, blockPartsHeader := crypto.CRandBytes(32), PartSetHeader{123, crypto.CRandBytes(32)}