diff --git a/blocks/signature.go b/blocks/signature.go
index 80b6c91d8..33f6f9a47 100644
--- a/blocks/signature.go
+++ b/blocks/signature.go
@@ -6,7 +6,7 @@ import (
 )
 
 type Signable interface {
-	GenDocument() []byte
+	Binary
 	GetSignature() Signature
 	SetSignature(Signature)
 }
diff --git a/blocks/tx.go b/blocks/tx.go
index c4f311ecc..e43f3b8b9 100644
--- a/blocks/tx.go
+++ b/blocks/tx.go
@@ -19,59 +19,56 @@ Validation Txs:
 */
 
 type Tx interface {
-	Type() byte
-	//IsValidation() bool
-	Binary
+	Signable
+	GetSequence() uint64
 }
 
 const (
 	// Account transactions
-	txTypeSend = byte(0x01)
-	txTypeName = byte(0x02)
+	TxTypeSend = byte(0x01)
+	TxTypeName = byte(0x02)
 
 	// Validation transactions
-	txTypeBond    = byte(0x11)
-	txTypeUnbond  = byte(0x12)
-	txTypeTimeout = byte(0x13)
-	txTypeDupeout = byte(0x14)
+	TxTypeBond    = byte(0x11)
+	TxTypeUnbond  = byte(0x12)
+	TxTypeTimeout = byte(0x13)
+	TxTypeDupeout = byte(0x14)
 )
 
 func ReadTx(r io.Reader, n *int64, err *error) Tx {
 	switch t := ReadByte(r, n, err); t {
-	case txTypeSend:
+	case TxTypeSend:
 		return &SendTx{
 			BaseTx: ReadBaseTx(r, n, err),
 			Fee:    ReadUInt64(r, n, err),
 			To:     ReadUInt64(r, n, err),
 			Amount: ReadUInt64(r, n, err),
 		}
-	case txTypeName:
+	case TxTypeName:
 		return &NameTx{
 			BaseTx: ReadBaseTx(r, n, err),
 			Fee:    ReadUInt64(r, n, err),
 			Name:   ReadString(r, n, err),
 			PubKey: ReadByteSlice(r, n, err),
 		}
-	case txTypeBond:
+	case TxTypeBond:
 		return &BondTx{
 			BaseTx:   ReadBaseTx(r, n, err),
 			Fee:      ReadUInt64(r, n, err),
 			UnbondTo: ReadUInt64(r, n, err),
-			Amount:   ReadUInt64(r, n, err),
 		}
-	case txTypeUnbond:
+	case TxTypeUnbond:
 		return &UnbondTx{
 			BaseTx: ReadBaseTx(r, n, err),
 			Fee:    ReadUInt64(r, n, err),
-			Amount: ReadUInt64(r, n, err),
 		}
-	case txTypeTimeout:
+	case TxTypeTimeout:
 		return &TimeoutTx{
 			BaseTx:    ReadBaseTx(r, n, err),
 			AccountId: ReadUInt64(r, n, err),
 			Penalty:   ReadUInt64(r, n, err),
 		}
-	case txTypeDupeout:
+	case TxTypeDupeout:
 		return &DupeoutTx{
 			BaseTx: ReadBaseTx(r, n, err),
 			VoteA:  *ReadVote(r, n, err),
@@ -103,6 +100,10 @@ func (tx BaseTx) WriteTo(w io.Writer) (n int64, err error) {
 	return
 }
 
+func (tx *BaseTx) GetSequence() uint64 {
+	return tx.Sequence
+}
+
 func (tx *BaseTx) GetSignature() Signature {
 	return tx.Signature
 }
@@ -120,12 +121,8 @@ type SendTx struct {
 	Amount uint64
 }
 
-func (tx *SendTx) Type() byte {
-	return txTypeSend
-}
-
 func (tx *SendTx) WriteTo(w io.Writer) (n int64, err error) {
-	WriteByte(w, tx.Type(), &n, &err)
+	WriteByte(w, TxTypeSend, &n, &err)
 	WriteBinary(w, tx.BaseTx, &n, &err)
 	WriteUInt64(w, tx.Fee, &n, &err)
 	WriteUInt64(w, tx.To, &n, &err)
@@ -142,12 +139,8 @@ type NameTx struct {
 	PubKey []byte
 }
 
-func (tx *NameTx) Type() byte {
-	return txTypeName
-}
-
 func (tx *NameTx) WriteTo(w io.Writer) (n int64, err error) {
-	WriteByte(w, tx.Type(), &n, &err)
+	WriteByte(w, TxTypeName, &n, &err)
 	WriteBinary(w, tx.BaseTx, &n, &err)
 	WriteUInt64(w, tx.Fee, &n, &err)
 	WriteString(w, tx.Name, &n, &err)
@@ -161,19 +154,13 @@ type BondTx struct {
 	BaseTx
 	Fee      uint64
 	UnbondTo uint64
-	Amount   uint64
-}
-
-func (tx *BondTx) Type() byte {
-	return txTypeBond
 }
 
 func (tx *BondTx) WriteTo(w io.Writer) (n int64, err error) {
-	WriteByte(w, tx.Type(), &n, &err)
+	WriteByte(w, TxTypeBond, &n, &err)
 	WriteBinary(w, tx.BaseTx, &n, &err)
 	WriteUInt64(w, tx.Fee, &n, &err)
 	WriteUInt64(w, tx.UnbondTo, &n, &err)
-	WriteUInt64(w, tx.Amount, &n, &err)
 	return
 }
 
@@ -181,19 +168,13 @@ func (tx *BondTx) WriteTo(w io.Writer) (n int64, err error) {
 
 type UnbondTx struct {
 	BaseTx
-	Fee    uint64
-	Amount uint64
-}
-
-func (tx *UnbondTx) Type() byte {
-	return txTypeUnbond
+	Fee uint64
 }
 
 func (tx *UnbondTx) WriteTo(w io.Writer) (n int64, err error) {
-	WriteByte(w, tx.Type(), &n, &err)
+	WriteByte(w, TxTypeUnbond, &n, &err)
 	WriteBinary(w, tx.BaseTx, &n, &err)
 	WriteUInt64(w, tx.Fee, &n, &err)
-	WriteUInt64(w, tx.Amount, &n, &err)
 	return
 }
 
@@ -205,12 +186,8 @@ type TimeoutTx struct {
 	Penalty   uint64
 }
 
-func (tx *TimeoutTx) Type() byte {
-	return txTypeTimeout
-}
-
 func (tx *TimeoutTx) WriteTo(w io.Writer) (n int64, err error) {
-	WriteByte(w, tx.Type(), &n, &err)
+	WriteByte(w, TxTypeTimeout, &n, &err)
 	WriteBinary(w, tx.BaseTx, &n, &err)
 	WriteUInt64(w, tx.AccountId, &n, &err)
 	WriteUInt64(w, tx.Penalty, &n, &err)
@@ -225,22 +202,10 @@ type DupeoutTx struct {
 	VoteB Vote
 }
 
-func (tx *DupeoutTx) Type() byte {
-	return txTypeDupeout
-}
-
 func (tx *DupeoutTx) WriteTo(w io.Writer) (n int64, err error) {
-	WriteByte(w, tx.Type(), &n, &err)
+	WriteByte(w, TxTypeDupeout, &n, &err)
 	WriteBinary(w, tx.BaseTx, &n, &err)
 	WriteBinary(w, &tx.VoteA, &n, &err)
 	WriteBinary(w, &tx.VoteB, &n, &err)
 	return
 }
-
-func (tx *DupeoutTx) GenDocument() []byte {
-	oldSig := tx.Signature
-	tx.Signature = Signature{}
-	doc := BinaryBytes(tx)
-	tx.Signature = oldSig
-	return doc
-}
diff --git a/blocks/vote.go b/blocks/vote.go
index babd58229..041657096 100644
--- a/blocks/vote.go
+++ b/blocks/vote.go
@@ -49,14 +49,6 @@ func (v *Vote) WriteTo(w io.Writer) (n int64, err error) {
 	return
 }
 
-func (v *Vote) GenDocument() []byte {
-	oldSig := v.Signature
-	v.Signature = Signature{}
-	doc := BinaryBytes(v)
-	v.Signature = oldSig
-	return doc
-}
-
 func (v *Vote) GetSignature() Signature {
 	return v.Signature
 }
diff --git a/consensus/consensus.go b/consensus/consensus.go
index 0d3ffdf3b..4e616ad5c 100644
--- a/consensus/consensus.go
+++ b/consensus/consensus.go
@@ -402,7 +402,7 @@ OUTER_LOOP:
 // Signs a vote document and broadcasts it.
 func (conR *ConsensusReactor) signAndBroadcastVote(rs *RoundState, vote *Vote) {
 	if rs.PrivValidator != nil {
-		rs.PrivValidator.SignVote(vote)
+		rs.PrivValidator.Sign(vote)
 		conR.conS.AddVote(vote)
 		msg := p2p.TypedMessage{msgTypeVote, vote}
 		conR.sw.Broadcast(VoteCh, msg)
diff --git a/consensus/pol.go b/consensus/pol.go
index ae34c48c9..1308b3744 100644
--- a/consensus/pol.go
+++ b/consensus/pol.go
@@ -45,8 +45,8 @@ func (pol *POL) WriteTo(w io.Writer) (n int64, err error) {
 func (pol *POL) Verify(vset *ValidatorSet) error {
 
 	talliedVotingPower := uint64(0)
-	voteDoc := (&Vote{Height: pol.Height, Round: pol.Round,
-		Type: VoteTypeBare, BlockHash: pol.BlockHash}).GenDocument()
+	voteDoc := BinaryBytes(&Vote{Height: pol.Height, Round: pol.Round,
+		Type: VoteTypeBare, BlockHash: pol.BlockHash})
 	seenValidators := map[uint64]struct{}{}
 
 	for _, sig := range pol.Votes {
@@ -59,7 +59,7 @@ func (pol *POL) Verify(vset *ValidatorSet) error {
 		if validator == nil {
 			return Errorf("Invalid validator for vote %v for POL %v", sig, pol)
 		}
-		if !validator.Verify(voteDoc, sig) {
+		if !validator.VerifyBytes(voteDoc, sig) {
 			return Errorf("Invalid signature for vote %v for POL %v", sig, pol)
 		}
 
@@ -80,9 +80,9 @@ func (pol *POL) Verify(vset *ValidatorSet) error {
 			return Errorf("Invalid validator for commit %v for POL %v", sig, pol)
 		}
 
-		commitDoc := (&Vote{Height: pol.Height, Round: round,
-			Type: VoteTypeCommit, BlockHash: pol.BlockHash}).GenDocument() // TODO cache
-		if !validator.Verify(commitDoc, sig) {
+		commitDoc := BinaryBytes(&Vote{Height: pol.Height, Round: round,
+			Type: VoteTypeCommit, BlockHash: pol.BlockHash}) // TODO cache
+		if !validator.VerifyBytes(commitDoc, sig) {
 			return Errorf("Invalid signature for commit %v for POL %v", sig, pol)
 		}
 
diff --git a/consensus/priv_validator.go b/consensus/priv_validator.go
index cb6c53538..c5152e228 100644
--- a/consensus/priv_validator.go
+++ b/consensus/priv_validator.go
@@ -13,14 +13,14 @@ type PrivValidator struct {
 	db *db_.LevelDB
 }
 
-// Double signing results in an error.
-func (pv *PrivValidator) SignProposal(proposal *Proposal) {
-	//TODO: prevent double signing.
-	pv.SignSignable(proposal)
-}
-
-// Double signing results in an error.
-func (pv *PrivValidator) SignVote(vote *Vote) {
-	//TODO: prevent double signing.
-	pv.SignSignable(vote)
+// Double signing results in a panic.
+func (pv *PrivValidator) Sign(o Signable) {
+	switch o.(type) {
+	case *Proposal:
+		//TODO: prevent double signing.
+		pv.PrivAccount.Sign(o.(*Proposal))
+	case *Vote:
+		//TODO: prevent double signing.
+		pv.PrivAccount.Sign(o.(*Vote))
+	}
 }
diff --git a/consensus/proposal.go b/consensus/proposal.go
index 2fb695042..ab87281a3 100644
--- a/consensus/proposal.go
+++ b/consensus/proposal.go
@@ -58,14 +58,6 @@ func (p *Proposal) WriteTo(w io.Writer) (n int64, err error) {
 	return
 }
 
-func (p *Proposal) GenDocument() []byte {
-	oldSig := p.Signature
-	p.Signature = Signature{}
-	doc := BinaryBytes(p)
-	p.Signature = oldSig
-	return doc
-}
-
 func (p *Proposal) GetSignature() Signature {
 	return p.Signature
 }
diff --git a/consensus/state.go b/consensus/state.go
index 3fd38e9d9..74b25218b 100644
--- a/consensus/state.go
+++ b/consensus/state.go
@@ -178,7 +178,7 @@ func (cs *ConsensusState) SetProposal(proposal *Proposal) error {
 	}
 
 	// Verify signature
-	if !cs.Proposer.Verify(proposal.GenDocument(), proposal.Signature) {
+	if !cs.Proposer.Verify(proposal) {
 		return ErrInvalidProposalSignature
 	}
 
@@ -220,7 +220,7 @@ func (cs *ConsensusState) MakeProposal() {
 	// Make proposal
 	proposal := NewProposal(cs.Height, cs.Round, blockPartSet.Total(), blockPartSet.RootHash(),
 		polPartSet.Total(), polPartSet.RootHash())
-	cs.PrivValidator.SignProposal(proposal)
+	cs.PrivValidator.Sign(proposal)
 
 	// Set fields
 	cs.Proposal = proposal
diff --git a/consensus/vote_set.go b/consensus/vote_set.go
index 39f49c00c..851b15ec8 100644
--- a/consensus/vote_set.go
+++ b/consensus/vote_set.go
@@ -69,7 +69,7 @@ func (vs *VoteSet) AddVote(vote *Vote) (bool, error) {
 	}
 
 	// Check signature.
-	if !val.Verify(vote.GenDocument(), vote.Signature) {
+	if !val.Verify(vote) {
 		// Bad signature.
 		return false, ErrVoteInvalidSignature
 	}
diff --git a/merkle/iavl_tree.go b/merkle/iavl_tree.go
index b2962a968..5fed69677 100644
--- a/merkle/iavl_tree.go
+++ b/merkle/iavl_tree.go
@@ -3,8 +3,6 @@ package merkle
 import (
 	"bytes"
 	"container/list"
-	. "github.com/tendermint/tendermint/binary"
-	. "github.com/tendermint/tendermint/common"
 )
 
 const defaultCacheCapacity = 1000 // TODO make configurable.
@@ -117,83 +115,6 @@ func (t *IAVLTree) Copy() Tree {
 
 //-----------------------------------------------------------------------------
 
-// TODO: make TypedTree work with the underlying tree to cache the decoded value.
-type TypedTree struct {
-	Tree       Tree
-	keyCodec   Codec
-	valueCodec Codec
-}
-
-func NewTypedTree(tree Tree, keyCodec, valueCodec Codec) *TypedTree {
-	return &TypedTree{
-		Tree:       tree,
-		keyCodec:   keyCodec,
-		valueCodec: valueCodec,
-	}
-}
-
-func (t *TypedTree) Has(key interface{}) bool {
-	bytes, err := t.keyCodec.Write(key)
-	if err != nil {
-		Panicf("Error from keyCodec: %v", err)
-	}
-	return t.Tree.Has(bytes)
-}
-
-func (t *TypedTree) Get(key interface{}) interface{} {
-	keyBytes, err := t.keyCodec.Write(key)
-	if err != nil {
-		Panicf("Error from keyCodec: %v", err)
-	}
-	valueBytes := t.Tree.Get(keyBytes)
-	if valueBytes == nil {
-		return nil
-	}
-	value, err := t.valueCodec.Read(valueBytes)
-	if err != nil {
-		Panicf("Error from valueCodec: %v", err)
-	}
-	return value
-}
-
-func (t *TypedTree) Set(key interface{}, value interface{}) bool {
-	keyBytes, err := t.keyCodec.Write(key)
-	if err != nil {
-		Panicf("Error from keyCodec: %v", err)
-	}
-	valueBytes, err := t.valueCodec.Write(value)
-	if err != nil {
-		Panicf("Error from valueCodec: %v", err)
-	}
-	return t.Tree.Set(keyBytes, valueBytes)
-}
-
-func (t *TypedTree) Remove(key interface{}) (interface{}, error) {
-	keyBytes, err := t.keyCodec.Write(key)
-	if err != nil {
-		Panicf("Error from keyCodec: %v", err)
-	}
-	valueBytes, err := t.Tree.Remove(keyBytes)
-	if valueBytes == nil {
-		return nil, err
-	}
-	value, err_ := t.valueCodec.Read(valueBytes)
-	if err_ != nil {
-		Panicf("Error from valueCodec: %v", err)
-	}
-	return value, err
-}
-
-func (t *TypedTree) Copy() *TypedTree {
-	return &TypedTree{
-		Tree:       t.Tree.Copy(),
-		keyCodec:   t.keyCodec,
-		valueCodec: t.valueCodec,
-	}
-}
-
-//-----------------------------------------------------------------------------
-
 type nodeElement struct {
 	node *IAVLNode
 	elem *list.Element
diff --git a/merkle/typed_tree.go b/merkle/typed_tree.go
new file mode 100644
index 000000000..efafc6b88
--- /dev/null
+++ b/merkle/typed_tree.go
@@ -0,0 +1,81 @@
+package merkle
+
+import (
+	. "github.com/tendermint/tendermint/binary"
+	. "github.com/tendermint/tendermint/common"
+)
+
+// TODO: make TypedTree work with the underlying tree to cache the decoded value.
+type TypedTree struct {
+	Tree       Tree
+	keyCodec   Codec
+	valueCodec Codec
+}
+
+func NewTypedTree(tree Tree, keyCodec, valueCodec Codec) *TypedTree {
+	return &TypedTree{
+		Tree:       tree,
+		keyCodec:   keyCodec,
+		valueCodec: valueCodec,
+	}
+}
+
+func (t *TypedTree) Has(key interface{}) bool {
+	bytes, err := t.keyCodec.Write(key)
+	if err != nil {
+		Panicf("Error from keyCodec: %v", err)
+	}
+	return t.Tree.Has(bytes)
+}
+
+func (t *TypedTree) Get(key interface{}) interface{} {
+	keyBytes, err := t.keyCodec.Write(key)
+	if err != nil {
+		Panicf("Error from keyCodec: %v", err)
+	}
+	valueBytes := t.Tree.Get(keyBytes)
+	if valueBytes == nil {
+		return nil
+	}
+	value, err := t.valueCodec.Read(valueBytes)
+	if err != nil {
+		Panicf("Error from valueCodec: %v", err)
+	}
+	return value
+}
+
+func (t *TypedTree) Set(key interface{}, value interface{}) bool {
+	keyBytes, err := t.keyCodec.Write(key)
+	if err != nil {
+		Panicf("Error from keyCodec: %v", err)
+	}
+	valueBytes, err := t.valueCodec.Write(value)
+	if err != nil {
+		Panicf("Error from valueCodec: %v", err)
+	}
+	return t.Tree.Set(keyBytes, valueBytes)
+}
+
+func (t *TypedTree) Remove(key interface{}) (interface{}, error) {
+	keyBytes, err := t.keyCodec.Write(key)
+	if err != nil {
+		Panicf("Error from keyCodec: %v", err)
+	}
+	valueBytes, err := t.Tree.Remove(keyBytes)
+	if valueBytes == nil {
+		return nil, err
+	}
+	value, err_ := t.valueCodec.Read(valueBytes)
+	if err_ != nil {
+		Panicf("Error from valueCodec: %v", err)
+	}
+	return value, err
+}
+
+func (t *TypedTree) Copy() *TypedTree {
+	return &TypedTree{
+		Tree:       t.Tree.Copy(),
+		keyCodec:   t.keyCodec,
+		valueCodec: t.valueCodec,
+	}
+}
diff --git a/state/account.go b/state/account.go
index 45aada2cf..91405209f 100644
--- a/state/account.go
+++ b/state/account.go
@@ -9,8 +9,9 @@ import (
 )
 
 const (
-	AccountBalanceStatusNominal = byte(0x00)
-	AccountBalanceStatusBonded  = byte(0x01)
+	AccountDetailStatusNominal   = byte(0x00)
+	AccountDetailStatusBonded    = byte(0x01)
+	AccountDetailStatusUnbonding = byte(0x02)
 )
 
 type Account struct {
@@ -31,7 +32,7 @@ func (account Account) WriteTo(w io.Writer) (n int64, err error) {
 	return
 }
 
-func (account Account) Verify(msg []byte, sig Signature) bool {
+func (account Account) VerifyBytes(msg []byte, sig Signature) bool {
 	if sig.SignerId != account.Id {
 		panic("account.id doesn't match sig.signerid")
 	}
@@ -44,32 +45,37 @@ func (account Account) Verify(msg []byte, sig Signature) bool {
 	return ok
 }
 
-func (account Account) VerifySignable(o Signable) bool {
-	msg := o.GenDocument()
+func (account Account) Verify(o Signable) bool {
 	sig := o.GetSignature()
-	return account.Verify(msg, sig)
+	o.SetSignature(Signature{}) // clear
+	msg := BinaryBytes(o)
+	o.SetSignature(sig) // restore
+	return account.VerifyBytes(msg, sig)
 }
 
 //-----------------------------------------------------------------------------
 
-type AccountBalance struct {
+type AccountDetail struct {
 	Account
-	Balance uint64
-	Status  byte
+	Sequence uint64
+	Balance  uint64
+	Status   byte
 }
 
-func ReadAccountBalance(r io.Reader, n *int64, err *error) *AccountBalance {
-	return &AccountBalance{
-		Account: ReadAccount(r, n, err),
-		Balance: ReadUInt64(r, n, err),
-		Status:  ReadByte(r, n, err),
+func ReadAccountDetail(r io.Reader, n *int64, err *error) *AccountDetail {
+	return &AccountDetail{
+		Account:  ReadAccount(r, n, err),
+		Sequence: ReadUInt64(r, n, err),
+		Balance:  ReadUInt64(r, n, err),
+		Status:   ReadByte(r, n, err),
 	}
 }
 
-func (accBal AccountBalance) WriteTo(w io.Writer) (n int64, err error) {
-	WriteBinary(w, accBal.Account, &n, &err)
-	WriteUInt64(w, accBal.Balance, &n, &err)
-	WriteByte(w, accBal.Status, &n, &err)
+func (accDet AccountDetail) WriteTo(w io.Writer) (n int64, err error) {
+	WriteBinary(w, accDet.Account, &n, &err)
+	WriteUInt64(w, accDet.Sequence, &n, &err)
+	WriteUInt64(w, accDet.Balance, &n, &err)
+	WriteByte(w, accDet.Status, &n, &err)
 	return
 }
 
@@ -94,7 +100,7 @@ func GenPrivAccount() *PrivAccount {
 	}
 }
 
-func (pa *PrivAccount) Sign(msg []byte) Signature {
+func (pa *PrivAccount) SignBytes(msg []byte) Signature {
 	signature := crypto.SignMessage(msg, pa.PrivKey, pa.PubKey)
 	sig := Signature{
 		SignerId: pa.Id,
@@ -103,8 +109,9 @@ func (pa *PrivAccount) Sign(msg []byte) Signature {
 	return sig
 }
 
-func (pa *PrivAccount) SignSignable(o Signable) {
-	msg := o.GenDocument()
-	sig := pa.Sign(msg)
+func (pa *PrivAccount) Sign(o Signable) {
+	o.SetSignature(Signature{}) // clear
+	msg := BinaryBytes(o)
+	sig := pa.SignBytes(msg)
 	o.SetSignature(sig)
 }
diff --git a/state/account_test.go b/state/account_test.go
index 528097052..a9af1761e 100644
--- a/state/account_test.go
+++ b/state/account_test.go
@@ -11,7 +11,7 @@ func TestSignAndValidate(t *testing.T) {
 	account := &privAccount.Account
 
 	msg := CRandBytes(128)
-	sig := privAccount.Sign(msg)
+	sig := privAccount.SignBytes(msg)
 	t.Logf("msg: %X, sig: %X", msg, sig)
 
 	// Test the signature
diff --git a/state/state.go b/state/state.go
index 395dde505..b5d26d613 100644
--- a/state/state.go
+++ b/state/state.go
@@ -12,62 +12,67 @@ import (
 )
 
 var (
+	ErrStateInvalidAccountId           = errors.New("Error State invalid account id")
+	ErrStateInvalidSignature           = errors.New("Error State invalid signature")
 	ErrStateInvalidSequenceNumber      = errors.New("Error State invalid sequence number")
+	ErrStateInvalidAccountState        = errors.New("Error State invalid account state")
 	ErrStateInvalidValidationStateHash = errors.New("Error State invalid ValidationStateHash")
 	ErrStateInvalidAccountStateHash    = errors.New("Error State invalid AccountStateHash")
+	ErrStateInsufficientFunds          = errors.New("Error State insufficient funds")
 
-	stateKey = []byte("stateKey")
+	stateKey      = []byte("stateKey")
+	minBondAmount = uint64(1) // TODO adjust
 )
 
-type accountBalanceCodec struct{}
+type accountDetailCodec struct{}
 
-func (abc accountBalanceCodec) Write(accBal interface{}) (accBalBytes []byte, err error) {
+func (abc accountDetailCodec) Write(accDet interface{}) (accDetBytes []byte, err error) {
 	w := new(bytes.Buffer)
-	_, err = accBal.(*AccountBalance).WriteTo(w)
+	_, err = accDet.(*AccountDetail).WriteTo(w)
 	return w.Bytes(), err
 }
 
-func (abc accountBalanceCodec) Read(accBalBytes []byte) (interface{}, error) {
-	n, err, r := new(int64), new(error), bytes.NewBuffer(accBalBytes)
-	return ReadAccountBalance(r, n, err), *err
+func (abc accountDetailCodec) Read(accDetBytes []byte) (interface{}, error) {
+	n, err, r := new(int64), new(error), bytes.NewBuffer(accDetBytes)
+	return ReadAccountDetail(r, n, err), *err
 }
 
 //-----------------------------------------------------------------------------
 
 // NOTE: not goroutine-safe.
 type State struct {
-	DB              DB
-	Height          uint32 // Last known block height
-	BlockHash       []byte // Last known block hash
-	CommitTime      time.Time
-	AccountBalances *merkle.TypedTree
-	Validators      *ValidatorSet
+	DB             DB
+	Height         uint32 // Last known block height
+	BlockHash      []byte // Last known block hash
+	CommitTime     time.Time
+	AccountDetails *merkle.TypedTree
+	Validators     *ValidatorSet
 }
 
-func GenesisState(db DB, genesisTime time.Time, accBals []*AccountBalance) *State {
+func GenesisState(db DB, genesisTime time.Time, accDets []*AccountDetail) *State {
 
 	// TODO: Use "uint64Codec" instead of BasicCodec
-	accountBalances := merkle.NewTypedTree(merkle.NewIAVLTree(db), BasicCodec, accountBalanceCodec{})
+	accountDetails := merkle.NewTypedTree(merkle.NewIAVLTree(db), BasicCodec, accountDetailCodec{})
 	validators := map[uint64]*Validator{}
 
-	for _, accBal := range accBals {
-		accountBalances.Set(accBal.Id, accBal)
-		validators[accBal.Id] = &Validator{
-			Account:     accBal.Account,
+	for _, accDet := range accDets {
+		accountDetails.Set(accDet.Id, accDet)
+		validators[accDet.Id] = &Validator{
+			Account:     accDet.Account,
 			BondHeight:  0,
-			VotingPower: accBal.Balance,
+			VotingPower: accDet.Balance,
 			Accum:       0,
 		}
 	}
 	validatorSet := NewValidatorSet(validators)
 
 	return &State{
-		DB:              db,
-		Height:          0,
-		BlockHash:       nil,
-		CommitTime:      genesisTime,
-		AccountBalances: accountBalances,
-		Validators:      validatorSet,
+		DB:             db,
+		Height:         0,
+		BlockHash:      nil,
+		CommitTime:     genesisTime,
+		AccountDetails: accountDetails,
+		Validators:     validatorSet,
 	}
 }
 
@@ -83,8 +88,8 @@ func LoadState(db DB) *State {
 		s.Height = ReadUInt32(reader, &n, &err)
 		s.CommitTime = ReadTime(reader, &n, &err)
 		s.BlockHash = ReadByteSlice(reader, &n, &err)
-		accountBalancesHash := ReadByteSlice(reader, &n, &err)
-		s.AccountBalances = merkle.NewTypedTree(merkle.LoadIAVLTreeFromHash(db, accountBalancesHash), BasicCodec, accountBalanceCodec{})
+		accountDetailsHash := ReadByteSlice(reader, &n, &err)
+		s.AccountDetails = merkle.NewTypedTree(merkle.LoadIAVLTreeFromHash(db, accountDetailsHash), BasicCodec, accountDetailCodec{})
 		var validators = map[uint64]*Validator{}
 		for reader.Len() > 0 {
 			validator := ReadValidator(reader, &n, &err)
@@ -103,14 +108,14 @@ func LoadState(db DB) *State {
 // is saved here.
 func (s *State) Save(commitTime time.Time) {
 	s.CommitTime = commitTime
-	s.AccountBalances.Tree.Save()
+	s.AccountDetails.Tree.Save()
 	var buf bytes.Buffer
 	var n int64
 	var err error
 	WriteUInt32(&buf, s.Height, &n, &err)
 	WriteTime(&buf, commitTime, &n, &err)
 	WriteByteSlice(&buf, s.BlockHash, &n, &err)
-	WriteByteSlice(&buf, s.AccountBalances.Tree.Hash(), &n, &err)
+	WriteByteSlice(&buf, s.AccountDetails.Tree.Hash(), &n, &err)
 	for _, validator := range s.Validators.Map() {
 		WriteBinary(&buf, validator, &n, &err)
 	}
@@ -122,26 +127,76 @@ func (s *State) Save(commitTime time.Time) {
 
 func (s *State) Copy() *State {
 	return &State{
-		DB:              s.DB,
-		Height:          s.Height,
-		CommitTime:      s.CommitTime,
-		BlockHash:       s.BlockHash,
-		AccountBalances: s.AccountBalances.Copy(),
-		Validators:      s.Validators.Copy(),
+		DB:             s.DB,
+		Height:         s.Height,
+		CommitTime:     s.CommitTime,
+		BlockHash:      s.BlockHash,
+		AccountDetails: s.AccountDetails.Copy(),
+		Validators:     s.Validators.Copy(),
 	}
 }
 
 // If the tx is invalid, an error will be returned.
 // Unlike AppendBlock(), state will not be altered.
 func (s *State) ExecTx(tx Tx) error {
-	/*
-		// Get the signer's incr
-		signerId := tx.Signature().SignerId
-		if mem.state.AccountSequence(signerId) != tx.Sequence() {
-			return ErrStateInvalidSequenceNumber
+	accDet := s.GetAccountDetail(tx.GetSignature().SignerId)
+	if accDet == nil {
+		return ErrStateInvalidAccountId
+	}
+	// Check signature
+	if !accDet.Verify(tx) {
+		return ErrStateInvalidSignature
+	}
+	// Check sequence
+	if tx.GetSequence() <= accDet.Sequence {
+		return ErrStateInvalidSequenceNumber
+	}
+	// Exec tx
+	switch tx.(type) {
+	case *SendTx:
+		stx := tx.(*SendTx)
+		toAccDet := s.GetAccountDetail(stx.To)
+		// Accounts must be nominal
+		if accDet.Status != AccountDetailStatusNominal {
+			return ErrStateInvalidAccountState
+		}
+		if toAccDet.Status != AccountDetailStatusNominal {
+			return ErrStateInvalidAccountState
+		}
+		// Check account balance
+		if accDet.Balance < stx.Fee+stx.Amount {
+			return ErrStateInsufficientFunds
+		}
+		// Check existence of destination account
+		if toAccDet == nil {
+			return ErrStateInvalidAccountId
 		}
-	*/
-	// XXX commit the tx
+		// Good!
+		accDet.Balance -= (stx.Fee + stx.Amount)
+		toAccDet.Balance += (stx.Amount)
+		s.SetAccountDetail(accDet)
+		s.SetAccountDetail(toAccDet)
+	//case *NameTx
+	case *BondTx:
+		btx := tx.(*BondTx)
+		// Account must be nominal
+		if accDet.Status != AccountDetailStatusNominal {
+			return ErrStateInvalidAccountState
+		}
+		// Check account balance
+		if accDet.Balance < minBondAmount {
+			return ErrStateInsufficientFunds
+		}
+		// TODO: max number of validators?
+		// Good!
+		accDet.Balance -= btx.Fee // remaining balance are bonded coins.
+		accDet.Status = AccountDetailStatusBonded
+		s.SetAccountDetail(accDet)
+		// XXX add validator
+	case *UnbondTx:
+	case *TimeoutTx:
+	case *DupeoutTx:
+	}
 	panic("Implement ExecTx()")
 	return nil
 }
@@ -170,7 +225,7 @@ func (s *State) AppendBlock(b *Block) error {
 	if !bytes.Equal(s.Validators.Hash(), b.ValidationStateHash) {
 		return ErrStateInvalidValidationStateHash
 	}
-	if !bytes.Equal(s.AccountBalances.Tree.Hash(), b.AccountStateHash) {
+	if !bytes.Equal(s.AccountDetails.Tree.Hash(), b.AccountStateHash) {
 		return ErrStateInvalidAccountStateHash
 	}
 
@@ -179,10 +234,15 @@ func (s *State) AppendBlock(b *Block) error {
 	return nil
 }
 
-func (s *State) AccountBalance(accountId uint64) *AccountBalance {
-	accBal := s.AccountBalances.Get(accountId)
-	if accBal == nil {
+func (s *State) GetAccountDetail(accountId uint64) *AccountDetail {
+	accDet := s.AccountDetails.Get(accountId)
+	if accDet == nil {
 		return nil
 	}
-	return accBal.(*AccountBalance)
+	return accDet.(*AccountDetail)
+}
+
+// Returns false if new, true if updated.
+func (s *State) SetAccountDetail(accDet *AccountDetail) (updated bool) {
+	return s.AccountDetails.Set(accDet.Id, accDet)
 }