diff --git a/call.go b/call.go
index aad89fa4..a516017c 100644
--- a/call.go
+++ b/call.go
@@ -47,7 +47,7 @@ import (
 // On error, it returns the error and indicates whether the call should be retried.
 //
 // TODO(zhaoq): Check whether the received message sequence is valid.
-func recvResponse(t transport.ClientTransport, c *callInfo, stream *transport.Stream, reply interface{}) error {
+func recvResponse(codec Codec, t transport.ClientTransport, c *callInfo, stream *transport.Stream, reply interface{}) error {
 	// Try to acquire header metadata from the server if there is any.
 	var err error
 	c.headerMD, err = stream.Header()
@@ -56,7 +56,7 @@ func recvResponse(t transport.ClientTransport, c *callInfo, stream *transport.St
 	}
 	p := &parser{s: stream}
 	for {
-		if err = recv(p, protoCodec{}, reply); err != nil {
+		if err = recv(p, codec, reply); err != nil {
 			if err == io.EOF {
 				break
 			}
@@ -68,7 +68,7 @@ func recvResponse(t transport.ClientTransport, c *callInfo, stream *transport.St
 }
 
 // sendRequest writes out various information of an RPC such as Context and Message.
-func sendRequest(ctx context.Context, callHdr *transport.CallHdr, t transport.ClientTransport, args interface{}, opts *transport.Options) (_ *transport.Stream, err error) {
+func sendRequest(ctx context.Context, codec Codec, callHdr *transport.CallHdr, t transport.ClientTransport, args interface{}, opts *transport.Options) (_ *transport.Stream, err error) {
 	stream, err := t.NewStream(ctx, callHdr)
 	if err != nil {
 		return nil, err
@@ -81,7 +81,7 @@ func sendRequest(ctx context.Context, callHdr *transport.CallHdr, t transport.Cl
 		}
 	}()
 	// TODO(zhaoq): Support compression.
-	outBuf, err := encode(protoCodec{}, args, compressionNone)
+	outBuf, err := encode(codec, args, compressionNone)
 	if err != nil {
 		return nil, transport.StreamErrorf(codes.Internal, "grpc: %v", err)
 	}
@@ -148,7 +148,7 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 			}
 			return toRPCErr(err)
 		}
-		stream, err = sendRequest(ctx, callHdr, t, args, topts)
+		stream, err = sendRequest(ctx, cc.dopts.codec, callHdr, t, args, topts)
 		if err != nil {
 			if _, ok := err.(transport.ConnectionError); ok {
 				lastErr = err
@@ -160,7 +160,7 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 			return toRPCErr(err)
 		}
 		// Receive the response
-		lastErr = recvResponse(t, &c, stream, reply)
+		lastErr = recvResponse(cc.dopts.codec, t, &c, stream, reply)
 		if _, ok := lastErr.(transport.ConnectionError); ok {
 			continue
 		}
diff --git a/clientconn.go b/clientconn.go
index 8ac660a4..6b78a768 100644
--- a/clientconn.go
+++ b/clientconn.go
@@ -55,29 +55,43 @@ var (
 	ErrClientConnTimeout = errors.New("grpc: timed out trying to connect")
 )
 
+// dialOptions configure a Dial call. dialOptions are set by the DialOption
+// values passed to Dial.
+type dialOptions struct {
+	codec Codec
+	copts transport.ConnectOptions
+}
+
 // DialOption configures how we set up the connection.
-type DialOption func(*transport.DialOptions)
+type DialOption func(*dialOptions)
+
+// WithCodec returns a DialOption which sets a codec for message marshaling and unmarshaling.
+func WithCodec(codec Codec) DialOption {
+	return func(o *dialOptions) {
+		o.codec = codec
+	}
+}
 
 // WithTransportCredentials returns a DialOption which configures a
 // connection level security credentials (e.g., TLS/SSL).
 func WithTransportCredentials(creds credentials.TransportAuthenticator) DialOption {
-	return func(o *transport.DialOptions) {
-		o.AuthOptions = append(o.AuthOptions, creds)
+	return func(o *dialOptions) {
+		o.copts.AuthOptions = append(o.copts.AuthOptions, creds)
 	}
 }
 
 // WithPerRPCCredentials returns a DialOption which sets
 // credentials which will place auth state on each outbound RPC.
 func WithPerRPCCredentials(creds credentials.Credentials) DialOption {
-	return func(o *transport.DialOptions) {
-		o.AuthOptions = append(o.AuthOptions, creds)
+	return func(o *dialOptions) {
+		o.copts.AuthOptions = append(o.copts.AuthOptions, creds)
 	}
 }
 
 // WithTimeout returns a DialOption that configures a timeout for dialing a client connection.
 func WithTimeout(d time.Duration) DialOption {
-	return func(o *transport.DialOptions) {
-		o.Timeout = d
+	return func(o *dialOptions) {
+		o.copts.Timeout = d
 	}
 }
 
@@ -94,6 +108,10 @@ func Dial(target string, opts ...DialOption) (*ClientConn, error) {
 	for _, opt := range opts {
 		opt(&cc.dopts)
 	}
+	if cc.dopts.codec == nil {
+		// Set the default codec.
+		cc.dopts.codec = &protoCodec{}
+	}
 	if err := cc.resetTransport(false); err != nil {
 		return nil, err
 	}
@@ -106,7 +124,7 @@ func Dial(target string, opts ...DialOption) (*ClientConn, error) {
 // ClientConn represents a client connection to an RPC service.
 type ClientConn struct {
 	target       string
-	dopts        transport.DialOptions
+	dopts        dialOptions
 	shutdownChan chan struct{}
 
 	mu sync.Mutex
@@ -140,23 +158,23 @@ func (cc *ClientConn) resetTransport(closeTransport bool) error {
 			t.Close()
 		}
 		// Adjust timeout for the current try.
-		dopts := cc.dopts
-		if dopts.Timeout < 0 {
+		copts := cc.dopts.copts
+		if copts.Timeout < 0 {
 			cc.Close()
 			return ErrClientConnTimeout
 		}
-		if dopts.Timeout > 0 {
-			dopts.Timeout -= time.Since(start)
-			if dopts.Timeout <= 0 {
+		if copts.Timeout > 0 {
+			copts.Timeout -= time.Since(start)
+			if copts.Timeout <= 0 {
 				cc.Close()
 				return ErrClientConnTimeout
 			}
 		}
-		newTransport, err := transport.NewClientTransport(cc.target, &dopts)
+		newTransport, err := transport.NewClientTransport(cc.target, &copts)
 		if err != nil {
 			sleepTime := backoff(retries)
 			// Fail early before falling into sleep.
-			if cc.dopts.Timeout > 0 && cc.dopts.Timeout < sleepTime+time.Since(start) {
+			if cc.dopts.copts.Timeout > 0 && cc.dopts.copts.Timeout < sleepTime+time.Since(start) {
 				cc.Close()
 				return ErrClientConnTimeout
 			}
diff --git a/server.go b/server.go
index e50f2b5f..d2369bf9 100644
--- a/server.go
+++ b/server.go
@@ -85,12 +85,19 @@ type Server struct {
 }
 
 type options struct {
+	codec Codec
 	maxConcurrentStreams uint32
 }
 
 // A ServerOption sets options.
 type ServerOption func(*options)
 
+func CustomCodec(codec Codec) ServerOption {
+	return func(o *options) {
+		o.codec = codec
+	}
+}
+
 // MaxConcurrentStreams returns an Option that will apply a limit on the number
 // of concurrent streams to each ServerTransport.
 func MaxConcurrentStreams(n uint32) ServerOption {
@@ -106,6 +113,10 @@ func NewServer(opt ...ServerOption) *Server {
 	for _, o := range opt {
 		o(&opts)
 	}
+	if opts.codec == nil {
+		// Set the default codec.
+		opts.codec = &protoCodec{}
+	}
 	return &Server{
 		lis:   make(map[net.Listener]bool),
 		opts:  opts,
@@ -203,7 +214,7 @@ func (s *Server) Serve(lis net.Listener) error {
 }
 
 func (s *Server) sendResponse(t transport.ServerTransport, stream *transport.Stream, msg interface{}, pf payloadFormat, opts *transport.Options) error {
-	p, err := encode(protoCodec{}, msg, pf)
+	p, err := encode(s.opts.codec, msg, pf)
 	if err != nil {
 		// This typically indicates a fatal issue (e.g., memory
 		// corruption or hardware faults) the application program
@@ -286,6 +297,7 @@ func (s *Server) processStreamingRPC(t transport.ServerTransport, stream *transp
 		t: t,
 		s: stream,
 		p: &parser{s: stream},
+		codec: s.opts.codec,
 	}
 	if appErr := sd.Handler(srv.server, ss); appErr != nil {
 		if err, ok := appErr.(rpcError); ok {
diff --git a/stream.go b/stream.go
index 625535a6..46e538f8 100644
--- a/stream.go
+++ b/stream.go
@@ -66,7 +66,7 @@ type Stream interface {
 	// side. On server side, it simply returns the error to the caller.
 	// SendMsg is called by generated code.
 	SendMsg(m interface{}) error
-	// RecvMsg blocks until it receives a proto message or the stream is
+	// RecvMsg blocks until it receives a message or the stream is
 	// done. On client side, it returns io.EOF when the stream is done. On
 	// any other error, it aborts the streama nd returns an RPC status. On
 	// server side, it simply returns the error to the caller.
@@ -116,6 +116,7 @@ func NewClientStream(ctx context.Context, desc *StreamDesc, cc *ClientConn, meth
 		s:    s,
 		p:    &parser{s: s},
 		desc: desc,
+		codec: cc.dopts.codec,
 	}, nil
 }
 
@@ -125,6 +126,7 @@ type clientStream struct {
 	s    *transport.Stream
 	p    *parser
 	desc *StreamDesc
+	codec Codec
 }
 
 func (cs *clientStream) Context() context.Context {
@@ -155,7 +157,7 @@ func (cs *clientStream) SendMsg(m interface{}) (err error) {
 		}
 		err = toRPCErr(err)
 	}()
-	out, err := encode(protoCodec{}, m, compressionNone)
+	out, err := encode(cs.codec, m, compressionNone)
 	if err != nil {
 		return transport.StreamErrorf(codes.Internal, "grpc: %v", err)
 	}
@@ -163,13 +165,13 @@ func (cs *clientStream) SendMsg(m interface{}) (err error) {
 }
 
 func (cs *clientStream) RecvMsg(m interface{}) (err error) {
-	err = recv(cs.p, protoCodec{}, m)
+	err = recv(cs.p, cs.codec, m)
 	if err == nil {
 		if !cs.desc.ClientStreams || cs.desc.ServerStreams {
 			return
 		}
 		// Special handling for client streaming rpc.
-		err = recv(cs.p, protoCodec{}, m)
+		err = recv(cs.p, cs.codec, m)
 		cs.t.CloseStream(cs.s, err)
 		if err == nil {
 			return toRPCErr(errors.New("grpc: client streaming protocol violation: get <nil>, want <EOF>"))
@@ -224,6 +226,7 @@ type serverStream struct {
 	t          transport.ServerTransport
 	s          *transport.Stream
 	p          *parser
+	codec      Codec
 	statusCode codes.Code
 	statusDesc string
 }
@@ -245,7 +248,7 @@ func (ss *serverStream) SetTrailer(md metadata.MD) {
 }
 
 func (ss *serverStream) SendMsg(m interface{}) error {
-	out, err := encode(protoCodec{}, m, compressionNone)
+	out, err := encode(ss.codec, m, compressionNone)
 	if err != nil {
 		err = transport.StreamErrorf(codes.Internal, "grpc: %v", err)
 		return err
@@ -254,5 +257,5 @@ func (ss *serverStream) SendMsg(m interface{}) error {
 }
 
 func (ss *serverStream) RecvMsg(m interface{}) error {
-	return recv(ss.p, protoCodec{}, m)
+	return recv(ss.p, ss.codec, m)
 }
diff --git a/transport/http2_client.go b/transport/http2_client.go
index 3c1044be..c61b4c5b 100644
--- a/transport/http2_client.go
+++ b/transport/http2_client.go
@@ -100,7 +100,7 @@ type http2Client struct {
 // newHTTP2Client constructs a connected ClientTransport to addr based on HTTP2
 // and starts to receive messages on it. Non-nil error returns if construction
 // fails.
-func newHTTP2Client(addr string, opts *DialOptions) (_ ClientTransport, err error) {
+func newHTTP2Client(addr string, opts *ConnectOptions) (_ ClientTransport, err error) {
 	var (
 		connErr error
 		conn    net.Conn
diff --git a/transport/transport.go b/transport/transport.go
index 56b31b87..a887857d 100644
--- a/transport/transport.go
+++ b/transport/transport.go
@@ -313,16 +313,16 @@ func NewServerTransport(protocol string, conn net.Conn, maxStreams uint32) (Serv
 	return newHTTP2Server(conn, maxStreams)
 }
 
-// DialOptions covers all relevant options for dialing a server.
-type DialOptions struct {
+// ConnectOptions covers all relevant options for dialing a server.
+type ConnectOptions struct {
 	Protocol    string
 	AuthOptions []credentials.Credentials
 	Timeout     time.Duration
 }
 
-// NewClientTransport establishes the transport with the required DialOptions
+// NewClientTransport establishes the transport with the required ConnectOptions
 // and returns it to the caller.
-func NewClientTransport(target string, opts *DialOptions) (ClientTransport, error) {
+func NewClientTransport(target string, opts *ConnectOptions) (ClientTransport, error) {
 	return newHTTP2Client(target, opts)
 }
 
diff --git a/transport/transport_test.go b/transport/transport_test.go
index 39792e4a..f017f1cb 100644
--- a/transport/transport_test.go
+++ b/transport/transport_test.go
@@ -182,12 +182,12 @@ func setUp(t *testing.T, useTLS bool, port int, maxStreams uint32, suspend bool)
 		if err != nil {
 			t.Fatalf("Failed to create credentials %v", err)
 		}
-		dopts := DialOptions{
+		dopts := ConnectOptions{
 			AuthOptions: []credentials.Credentials{creds},
 		}
 		ct, connErr = NewClientTransport(addr, &dopts)
 	} else {
-		ct, connErr = NewClientTransport(addr, &DialOptions{})
+		ct, connErr = NewClientTransport(addr, &ConnectOptions{})
 	}
 	if connErr != nil {
 		t.Fatalf("failed to create transport: %v", connErr)