diff --git a/consensus/istanbul/validator/default.go b/consensus/istanbul/validator/default.go
new file mode 100644
index 0000000000..17edda5521
--- /dev/null
+++ b/consensus/istanbul/validator/default.go
@@ -0,0 +1,201 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package validator
+
+import (
+	"math"
+	"reflect"
+	"sort"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus/istanbul"
+)
+
+type defaultValidator struct {
+	address common.Address
+}
+
+func (val *defaultValidator) Address() common.Address {
+	return val.address
+}
+
+func (val *defaultValidator) String() string {
+	return val.Address().String()
+}
+
+// ----------------------------------------------------------------------------
+
+type defaultSet struct {
+	validators istanbul.Validators
+	policy     istanbul.ProposerPolicy
+
+	proposer    istanbul.Validator
+	validatorMu sync.RWMutex
+	selector    istanbul.ProposalSelector
+}
+
+func newDefaultSet(addrs []common.Address, policy istanbul.ProposerPolicy) *defaultSet {
+	valSet := &defaultSet{}
+
+	valSet.policy = policy
+	// init validators
+	valSet.validators = make([]istanbul.Validator, len(addrs))
+	for i, addr := range addrs {
+		valSet.validators[i] = New(addr)
+	}
+	// sort validator
+	sort.Sort(valSet.validators)
+	// init proposer
+	if valSet.Size() > 0 {
+		valSet.proposer = valSet.GetByIndex(0)
+	}
+	valSet.selector = roundRobinProposer
+	if policy == istanbul.Sticky {
+		valSet.selector = stickyProposer
+	}
+
+	return valSet
+}
+
+func (valSet *defaultSet) Size() int {
+	valSet.validatorMu.RLock()
+	defer valSet.validatorMu.RUnlock()
+	return len(valSet.validators)
+}
+
+func (valSet *defaultSet) List() []istanbul.Validator {
+	valSet.validatorMu.RLock()
+	defer valSet.validatorMu.RUnlock()
+	return valSet.validators
+}
+
+func (valSet *defaultSet) GetByIndex(i uint64) istanbul.Validator {
+	valSet.validatorMu.RLock()
+	defer valSet.validatorMu.RUnlock()
+	if i < uint64(valSet.Size()) {
+		return valSet.validators[i]
+	}
+	return nil
+}
+
+func (valSet *defaultSet) GetByAddress(addr common.Address) (int, istanbul.Validator) {
+	for i, val := range valSet.List() {
+		if addr == val.Address() {
+			return i, val
+		}
+	}
+	return -1, nil
+}
+
+func (valSet *defaultSet) GetProposer() istanbul.Validator {
+	return valSet.proposer
+}
+
+func (valSet *defaultSet) IsProposer(address common.Address) bool {
+	_, val := valSet.GetByAddress(address)
+	return reflect.DeepEqual(valSet.GetProposer(), val)
+}
+
+func (valSet *defaultSet) CalcProposer(lastProposer common.Address, round uint64) {
+	valSet.validatorMu.RLock()
+	defer valSet.validatorMu.RUnlock()
+	valSet.proposer = valSet.selector(valSet, lastProposer, round)
+}
+
+func calcSeed(valSet istanbul.ValidatorSet, proposer common.Address, round uint64) uint64 {
+	offset := 0
+	if idx, val := valSet.GetByAddress(proposer); val != nil {
+		offset = idx
+	}
+	return uint64(offset) + round
+}
+
+func emptyAddress(addr common.Address) bool {
+	return addr == common.Address{}
+}
+
+func roundRobinProposer(valSet istanbul.ValidatorSet, proposer common.Address, round uint64) istanbul.Validator {
+	if valSet.Size() == 0 {
+		return nil
+	}
+	seed := uint64(0)
+	if emptyAddress(proposer) {
+		seed = round
+	} else {
+		seed = calcSeed(valSet, proposer, round) + 1
+	}
+	pick := seed % uint64(valSet.Size())
+	return valSet.GetByIndex(pick)
+}
+
+func stickyProposer(valSet istanbul.ValidatorSet, proposer common.Address, round uint64) istanbul.Validator {
+	if valSet.Size() == 0 {
+		return nil
+	}
+	seed := uint64(0)
+	if emptyAddress(proposer) {
+		seed = round
+	} else {
+		seed = calcSeed(valSet, proposer, round)
+	}
+	pick := seed % uint64(valSet.Size())
+	return valSet.GetByIndex(pick)
+}
+
+func (valSet *defaultSet) AddValidator(address common.Address) bool {
+	valSet.validatorMu.Lock()
+	defer valSet.validatorMu.Unlock()
+	for _, v := range valSet.validators {
+		if v.Address() == address {
+			return false
+		}
+	}
+	valSet.validators = append(valSet.validators, New(address))
+	// TODO: we may not need to re-sort it again
+	// sort validator
+	sort.Sort(valSet.validators)
+	return true
+}
+
+func (valSet *defaultSet) RemoveValidator(address common.Address) bool {
+	valSet.validatorMu.Lock()
+	defer valSet.validatorMu.Unlock()
+
+	for i, v := range valSet.validators {
+		if v.Address() == address {
+			valSet.validators = append(valSet.validators[:i], valSet.validators[i+1:]...)
+			return true
+		}
+	}
+	return false
+}
+
+func (valSet *defaultSet) Copy() istanbul.ValidatorSet {
+	valSet.validatorMu.RLock()
+	defer valSet.validatorMu.RUnlock()
+
+	addresses := make([]common.Address, 0, len(valSet.validators))
+	for _, v := range valSet.validators {
+		addresses = append(addresses, v.Address())
+	}
+	return NewSet(addresses, valSet.policy)
+}
+
+func (valSet *defaultSet) F() int { return int(math.Ceil(float64(valSet.Size())/3)) - 1 }
+
+func (valSet *defaultSet) Policy() istanbul.ProposerPolicy { return valSet.policy }
diff --git a/consensus/istanbul/validator/default_test.go b/consensus/istanbul/validator/default_test.go
new file mode 100644
index 0000000000..987ed12c84
--- /dev/null
+++ b/consensus/istanbul/validator/default_test.go
@@ -0,0 +1,208 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package validator
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus/istanbul"
+	"github.com/ethereum/go-ethereum/crypto"
+)
+
+var (
+	testAddress  = "70524d664ffe731100208a0154e556f9bb679ae6"
+	testAddress2 = "b37866a925bccd69cfa98d43b510f1d23d78a851"
+)
+
+func TestValidatorSet(t *testing.T) {
+	testNewValidatorSet(t)
+	testNormalValSet(t)
+	testEmptyValSet(t)
+	testStickyProposer(t)
+	testAddAndRemoveValidator(t)
+}
+
+func testNewValidatorSet(t *testing.T) {
+	var validators []istanbul.Validator
+	const ValCnt = 100
+
+	// Create 100 validators with random addresses
+	b := []byte{}
+	for i := 0; i < ValCnt; i++ {
+		key, _ := crypto.GenerateKey()
+		addr := crypto.PubkeyToAddress(key.PublicKey)
+		val := New(addr)
+		validators = append(validators, val)
+		b = append(b, val.Address().Bytes()...)
+	}
+
+	// Create ValidatorSet
+	valSet := NewSet(ExtractValidators(b), istanbul.RoundRobin)
+	if valSet == nil {
+		t.Errorf("the validator byte array cannot be parsed")
+		t.FailNow()
+	}
+
+	// Check validators sorting: should be in ascending order
+	for i := 0; i < ValCnt-1; i++ {
+		val := valSet.GetByIndex(uint64(i))
+		nextVal := valSet.GetByIndex(uint64(i + 1))
+		if strings.Compare(val.String(), nextVal.String()) >= 0 {
+			t.Errorf("validator set is not sorted in ascending order")
+		}
+	}
+}
+
+func testNormalValSet(t *testing.T) {
+	b1 := common.Hex2Bytes(testAddress)
+	b2 := common.Hex2Bytes(testAddress2)
+	addr1 := common.BytesToAddress(b1)
+	addr2 := common.BytesToAddress(b2)
+	val1 := New(addr1)
+	val2 := New(addr2)
+
+	valSet := newDefaultSet([]common.Address{addr1, addr2}, istanbul.RoundRobin)
+	if valSet == nil {
+		t.Errorf("the format of validator set is invalid")
+		t.FailNow()
+	}
+
+	// check size
+	if size := valSet.Size(); size != 2 {
+		t.Errorf("the size of validator set is wrong: have %v, want 2", size)
+	}
+	// test get by index
+	if val := valSet.GetByIndex(uint64(0)); !reflect.DeepEqual(val, val1) {
+		t.Errorf("validator mismatch: have %v, want %v", val, val1)
+	}
+	// test get by invalid index
+	if val := valSet.GetByIndex(uint64(2)); val != nil {
+		t.Errorf("validator mismatch: have %v, want nil", val)
+	}
+	// test get by address
+	if _, val := valSet.GetByAddress(addr2); !reflect.DeepEqual(val, val2) {
+		t.Errorf("validator mismatch: have %v, want %v", val, val2)
+	}
+	// test get by invalid address
+	invalidAddr := common.HexToAddress("0x9535b2e7faaba5288511d89341d94a38063a349b")
+	if _, val := valSet.GetByAddress(invalidAddr); val != nil {
+		t.Errorf("validator mismatch: have %v, want nil", val)
+	}
+	// test get proposer
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val1) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val1)
+	}
+	// test calculate proposer
+	lastProposer := addr1
+	valSet.CalcProposer(lastProposer, uint64(0))
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val2) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val2)
+	}
+	valSet.CalcProposer(lastProposer, uint64(3))
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val1) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val1)
+	}
+	// test empty last proposer
+	lastProposer = common.Address{}
+	valSet.CalcProposer(lastProposer, uint64(3))
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val2) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val2)
+	}
+}
+
+func testEmptyValSet(t *testing.T) {
+	valSet := NewSet(ExtractValidators([]byte{}), istanbul.RoundRobin)
+	if valSet == nil {
+		t.Errorf("validator set should not be nil")
+	}
+}
+
+func testAddAndRemoveValidator(t *testing.T) {
+	valSet := NewSet(ExtractValidators([]byte{}), istanbul.RoundRobin)
+	if !valSet.AddValidator(common.StringToAddress(string(2))) {
+		t.Error("the validator should be added")
+	}
+	if valSet.AddValidator(common.StringToAddress(string(2))) {
+		t.Error("the existing validator should not be added")
+	}
+	valSet.AddValidator(common.StringToAddress(string(1)))
+	valSet.AddValidator(common.StringToAddress(string(0)))
+	if len(valSet.List()) != 3 {
+		t.Error("the size of validator set should be 3")
+	}
+
+	for i, v := range valSet.List() {
+		expected := common.StringToAddress(string(i))
+		if v.Address() != expected {
+			t.Errorf("the order of validators is wrong: have %v, want %v", v.Address().Hex(), expected.Hex())
+		}
+	}
+
+	if !valSet.RemoveValidator(common.StringToAddress(string(2))) {
+		t.Error("the validator should be removed")
+	}
+	if valSet.RemoveValidator(common.StringToAddress(string(2))) {
+		t.Error("the non-existing validator should not be removed")
+	}
+	if len(valSet.List()) != 2 {
+		t.Error("the size of validator set should be 2")
+	}
+	valSet.RemoveValidator(common.StringToAddress(string(1)))
+	if len(valSet.List()) != 1 {
+		t.Error("the size of validator set should be 1")
+	}
+	valSet.RemoveValidator(common.StringToAddress(string(0)))
+	if len(valSet.List()) != 0 {
+		t.Error("the size of validator set should be 0")
+	}
+}
+
+func testStickyProposer(t *testing.T) {
+	b1 := common.Hex2Bytes(testAddress)
+	b2 := common.Hex2Bytes(testAddress2)
+	addr1 := common.BytesToAddress(b1)
+	addr2 := common.BytesToAddress(b2)
+	val1 := New(addr1)
+	val2 := New(addr2)
+
+	valSet := newDefaultSet([]common.Address{addr1, addr2}, istanbul.Sticky)
+
+	// test get proposer
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val1) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val1)
+	}
+	// test calculate proposer
+	lastProposer := addr1
+	valSet.CalcProposer(lastProposer, uint64(0))
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val1) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val1)
+	}
+
+	valSet.CalcProposer(lastProposer, uint64(1))
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val2) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val2)
+	}
+	// test empty last proposer
+	lastProposer = common.Address{}
+	valSet.CalcProposer(lastProposer, uint64(3))
+	if val := valSet.GetProposer(); !reflect.DeepEqual(val, val2) {
+		t.Errorf("proposer mismatch: have %v, want %v", val, val2)
+	}
+}
diff --git a/consensus/istanbul/validator/validator.go b/consensus/istanbul/validator/validator.go
new file mode 100644
index 0000000000..9a1e15c2d8
--- /dev/null
+++ b/consensus/istanbul/validator/validator.go
@@ -0,0 +1,47 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package validator
+
+import (
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus/istanbul"
+)
+
+func New(addr common.Address) istanbul.Validator {
+	return &defaultValidator{
+		address: addr,
+	}
+}
+
+func NewSet(addrs []common.Address, policy istanbul.ProposerPolicy) istanbul.ValidatorSet {
+	return newDefaultSet(addrs, policy)
+}
+
+func ExtractValidators(extraData []byte) []common.Address {
+	// get the validator addresses
+	addrs := make([]common.Address, (len(extraData) / common.AddressLength))
+	for i := 0; i < len(addrs); i++ {
+		copy(addrs[i][:], extraData[i*common.AddressLength:])
+	}
+
+	return addrs
+}
+
+// Check whether the extraData is presented in prescribed form
+func ValidExtraData(extraData []byte) bool {
+	return len(extraData)%common.AddressLength == 0
+}