diff --git a/clientv3/kv.go b/clientv3/kv.go
new file mode 100644
index 000000000..16cb2a602
--- /dev/null
+++ b/clientv3/kv.go
@@ -0,0 +1,99 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package clientv3
+
+type KV interface {
+	// PUT puts a key-value pair into etcd.
+	// Note that key,value can be plain bytes array and string is
+	// an immutable representation of that bytes array.
+	// To get a string of bytes, do string([]byte(0x10, 0x20)).
+	Put(key, val string) (PutResponse, error)
+
+	// Range gets the keys [key, end) in the range at rev.
+	// If revev <=0, range gets the keys at currentRev.
+	// Limit limits the number of keys returned.
+	// If the required rev is compacted, ErrCompacted will be returned.
+	Range(key, end string, limit, rev int64, sort SortOption) (RangeResponse, error)
+
+	// Get is like Range. A shortcut for ranging single key like [key, key+1).
+	Get(key, limit, rev int64) (RangeResponse, error)
+
+	// DeleteRange deletes the given range [key, end).
+	DeleteRange(key, end string) (DeleteRangeResponse, error)
+
+	// Delete is like DeleteRange. A shortcut for deleting single key like [key, key+1).
+	Delete(key string) (DeleteRangeResponse, error)
+
+	// Compact compacts etcd KV history before the given rev.
+	Compact(rev int64) error
+
+	// Txn creates a transaction.
+	Txn() Txn
+}
+
+//
+// Tx.If(
+//  CmpValue(k1, ">", v1),
+//  CmpVersion(k1, "=", 2)
+// ).Then(
+//  OpPut(k2,v2), OpPut(k3,v3)
+// ).Else(
+//  OpPut(k4,v4), OpPut(k5,v5)
+// ).Commit()
+type Txn interface {
+	// If takes a list of comparison. If all comparisons passed in succeed,
+	// the operations passed into Then() will be executed. Or the operations
+	// passed into Else() will be executed.
+	If(cs ...Compare) Txn
+
+	// Then takes a list of operations. The Ops list will be executed, if the
+	// comparisons passed in If() succeed.
+	Then(ops ...Op) Txn
+
+	// Else takes a list of operations. The Ops list will be executed, if the
+	// comparisons passed in If() fail.
+	Else(ops ...Op) Txn
+
+	// Commit tries to commit the transaction.
+	Commit() (TxnResponse, error)
+
+	// TODO: add a Do for shortcut the txn without any condition?
+}
+
+type Compare struct {
+}
+
+type Op struct {
+}
+
+type PutResponse struct {
+}
+
+type DeleteRangeResponse struct {
+}
+
+type RangeResponse struct {
+}
+
+type TxnResponse struct {
+}
+
+type SortTarget int
+type SortOrder int
+
+type SortOption struct {
+	Target SortTarget
+	Order  SortOrder
+}