diff --git a/endpoint_stream.go b/endpoint_stream.go
index b9a2717..138aebc 100644
--- a/endpoint_stream.go
+++ b/endpoint_stream.go
@@ -14,7 +14,7 @@
 
 package gousb
 
-func (e *endpoint) newStream(size, count int, submit bool) (*stream, error) {
+func (e *endpoint) newStream(size, count int) (*stream, error) {
 	var ts []transferIntf
 	for i := 0; i < count; i++ {
 		t, err := newUSBTransfer(e.ctx, e.h, &e.Desc, size, e.Timeout)
@@ -26,7 +26,7 @@ func (e *endpoint) newStream(size, count int, submit bool) (*stream, error) {
 		}
 		ts = append(ts, t)
 	}
-	return newStream(ts, submit), nil
+	return newStream(ts), nil
 }
 
 // NewStream prepares a new read stream that will keep reading data from the
@@ -36,9 +36,23 @@ func (e *endpoint) newStream(size, count int, submit bool) (*stream, error) {
 // By keeping multiple transfers active at the same time, a Stream reduces
 // the latency between subsequent transfers and increases reading throughput.
 func (e *InEndpoint) NewStream(size, count int) (*ReadStream, error) {
-	s, err := e.newStream(size, count, true)
+	s, err := e.newStream(size, count)
 	if err != nil {
 		return nil, err
 	}
-	return &ReadStream{s}, nil
+	s.submitAll()
+	return &ReadStream{s: s}, nil
+}
+
+// NewStream prepares a new write stream that will write data in the background.
+// Size defines a buffer size for a single write transaction and count
+// defines how many transactions may be active at any time.
+// By buffering the writes, a Stream reduces the latency between subsequent
+// transfers and increases writing throughput.
+func (e *OutEndpoint) NewStream(size, count int) (*WriteStream, error) {
+	s, err := e.newStream(size, count)
+	if err != nil {
+		return nil, err
+	}
+	return &WriteStream{s: s}, nil
 }
diff --git a/endpoint_stream_test.go b/endpoint_stream_test.go
index 51e14b5..c7418be 100644
--- a/endpoint_stream_test.go
+++ b/endpoint_stream_test.go
@@ -27,10 +27,11 @@ func TestEndpointReadStream(t *testing.T) {
 	}()
 
 	goodTransfers := 7
+	done := make(chan struct{})
 	go func() {
 		var num int
 		for {
-			xfr := lib.waitForSubmitted()
+			xfr := lib.waitForSubmitted(done)
 			if xfr == nil {
 				return
 			}
@@ -83,4 +84,80 @@ func TestEndpointReadStream(t *testing.T) {
 	if got != want {
 		t.Errorf("stream.Read(): read %d bytes, want %d", got, want)
 	}
+	close(done)
+}
+
+func TestEndpointWriteStream(t *testing.T) {
+	t.Parallel()
+	lib := newFakeLibusb()
+	ctx := newContextWithImpl(lib)
+	defer func() {
+		if err := ctx.Close(); err != nil {
+			t.Errorf("Context.Close: %v", err)
+		}
+	}()
+
+	done := make(chan struct{})
+	total := 0
+	num := 0
+	go func() {
+		for {
+			xfr := lib.waitForSubmitted(done)
+			if xfr == nil {
+				return
+			}
+			xfr.length = len(xfr.buf)
+			xfr.status = TransferCompleted
+			xfr.done <- struct{}{}
+			num++
+			total += xfr.length
+		}
+	}()
+
+	dev, err := ctx.OpenDeviceWithVIDPID(0x9999, 0x0001)
+	if err != nil {
+		t.Fatalf("OpenDeviceWithVIDPID(9999, 0001): %v", err)
+	}
+	defer dev.Close()
+	cfg, err := dev.Config(1)
+	if err != nil {
+		t.Fatalf("%s.Config(1): %v", dev, err)
+	}
+	defer cfg.Close()
+	intf, err := cfg.Interface(0, 0)
+	if err != nil {
+		t.Fatalf("%s.Interface(0, 0): %v", cfg, err)
+	}
+	defer intf.Close()
+	ep, err := intf.OutEndpoint(1)
+	if err != nil {
+		t.Fatalf("%s.Endpoint(1): %v", intf, err)
+	}
+	pktSize := 1024
+	stream, err := ep.NewStream(pktSize, 5)
+	if err != nil {
+		t.Fatalf("%s.NewStream(%d, 5): %v", ep, pktSize, err)
+	}
+	defer stream.Close()
+	for i := 0; i < 5; i++ {
+		if n, err := stream.Write(make([]byte, pktSize*2)); err != nil {
+			t.Fatalf("stream.Write: got error %v", err)
+		} else if n != pktSize*2 {
+			t.Fatalf("stream.Write: %d, want %d", n, pktSize*2)
+		}
+	}
+	want := pktSize * 10
+	if err := stream.Close(); err != nil {
+		t.Fatalf("stream.Close: got error %v", err)
+	}
+	if got := stream.Written(); got != want {
+		t.Errorf("stream.Written: got %d, want %d", got, want)
+	}
+	done <- struct{}{}
+	if num != 10 {
+		t.Errorf("received transfers: got %d, want %d", num, 10)
+	}
+	if total != want {
+		t.Errorf("received data: got %d, want %d", total, want)
+	}
 }
diff --git a/endpoint_test.go b/endpoint_test.go
index 7c1def0..4841121 100644
--- a/endpoint_test.go
+++ b/endpoint_test.go
@@ -100,7 +100,7 @@ func TestEndpoint(t *testing.T) {
 			ep := &endpoint{h: nil, ctx: ctx, InterfaceSetting: epData.intf, Desc: epData.ei}
 			if tc.wantSubmit {
 				go func() {
-					fakeT := lib.waitForSubmitted()
+					fakeT := lib.waitForSubmitted(nil)
 					fakeT.length = tc.ret
 					fakeT.status = tc.status
 					close(fakeT.done)
@@ -208,7 +208,7 @@ func TestEndpointInOut(t *testing.T) {
 	}
 	dataTransferred := 100
 	go func() {
-		fakeT := lib.waitForSubmitted()
+		fakeT := lib.waitForSubmitted(nil)
 		fakeT.length = dataTransferred
 		fakeT.status = TransferCompleted
 		close(fakeT.done)
@@ -232,7 +232,7 @@ func TestEndpointInOut(t *testing.T) {
 		t.Fatalf("%s.OutEndpoint(1): got error %v, want nil", intf, err)
 	}
 	go func() {
-		fakeT := lib.waitForSubmitted()
+		fakeT := lib.waitForSubmitted(nil)
 		fakeT.length = dataTransferred
 		fakeT.status = TransferCompleted
 		close(fakeT.done)
diff --git a/fakelibusb_test.go b/fakelibusb_test.go
index 338d3f2..5774d90 100644
--- a/fakelibusb_test.go
+++ b/fakelibusb_test.go
@@ -192,8 +192,16 @@ func (f *fakeLibusb) setIsoPacketLengths(*libusbTransfer, uint32) {}
 
 // waitForSubmitted can be used by tests to define custom behavior of the transfers submitted on the USB bus.
 // TODO(sebek): add fields in fakeTransfer to differentiate between different devices/endpoints used concurrently.
-func (f *fakeLibusb) waitForSubmitted() *fakeTransfer {
-	return <-f.submitted
+func (f *fakeLibusb) waitForSubmitted(done <-chan struct{}) *fakeTransfer {
+	select {
+	case t, ok := <-f.submitted:
+		if !ok {
+			return nil
+		}
+		return t
+	case <-done:
+		return nil
+	}
 }
 
 // empty can be used to confirm that all transfers were cleaned up.
diff --git a/transfer_stream.go b/transfer_stream.go
index 6e294fb..b28f1d2 100644
--- a/transfer_stream.go
+++ b/transfer_stream.go
@@ -27,18 +27,54 @@ type transferIntf interface {
 type stream struct {
 	// a fifo of USB transfers.
 	transfers chan transferIntf
-	// current holds the last transfer to return.
-	current transferIntf
-	// total/used are the number of all/used bytes in the current transfer.
-	total, used int
-	// delayedErr is the delayed error, returned to the user after all
-	// remaining data was read.
-	delayedErr error
+	// err is the first encountered error, returned to the user.
+	err error
+	// finished is true if transfers has been already closed.
+	finished bool
 }
 
-func (s *stream) setDelayedErr(err error) {
-	if s.delayedErr == nil {
-		s.delayedErr = err
+func (s *stream) gotError(err error) {
+	if s.err == nil {
+		s.err = err
+	}
+}
+
+func (s *stream) noMore() {
+	if !s.finished {
+		close(s.transfers)
+		s.finished = true
+	}
+}
+
+func (s *stream) submitAll() {
+	count := len(s.transfers)
+	var all []transferIntf
+	for i := 0; i < count; i++ {
+		all = append(all, <-s.transfers)
+	}
+	for _, t := range all {
+		if err := t.submit(); err != nil {
+			t.free()
+			s.gotError(err)
+			s.noMore()
+			return
+		}
+		s.transfers <- t
+	}
+	return
+}
+
+func (s *stream) flushRemaining() {
+	s.noMore()
+	for t := range s.transfers {
+		t.cancel()
+		t.wait()
+		t.free()
+	}
+}
+
+func (s *stream) done() {
+	if s.err == nil {
 		close(s.transfers)
 	}
 }
@@ -52,6 +88,10 @@ func (s *stream) setDelayedErr(err error) {
 // data is left, io.EOF is returned.
 type ReadStream struct {
 	s *stream
+	// current holds the last transfer to return.
+	current transferIntf
+	// total/used are the number of all/used bytes in the current transfer.
+	total, used int
 }
 
 // Read reads data from the transfer stream.
@@ -60,56 +100,49 @@ type ReadStream struct {
 // After a non-nil error is returned, all subsequent attempts to read will
 // return io.ErrClosedPipe.
 // Read cannot be called concurrently with other Read or Close.
-func (r ReadStream) Read(p []byte) (int, error) {
-	s := r.s
-	if s.transfers == nil {
+func (r *ReadStream) Read(p []byte) (int, error) {
+	if r.s.transfers == nil {
 		return 0, io.ErrClosedPipe
 	}
-	if s.current == nil {
-		t, ok := <-s.transfers
+	if r.current == nil {
+		t, ok := <-r.s.transfers
 		if !ok {
 			// no more transfers in flight
-			s.transfers = nil
-			return 0, s.delayedErr
+			r.s.transfers = nil
+			return 0, r.s.err
 		}
 		n, err := t.wait()
 		if err != nil {
 			// wait error aborts immediately, all remaining data is invalid.
 			t.free()
-			if s.delayedErr == nil {
-				close(s.transfers)
-			}
-			for t := range s.transfers {
-				t.cancel()
-				t.wait()
-				t.free()
-			}
-			s.transfers = nil
+			r.s.flushRemaining()
+			r.s.transfers = nil
 			return n, err
 		}
-		s.current = t
-		s.total = n
-		s.used = 0
+		r.current = t
+		r.total = n
+		r.used = 0
 	}
-	use := s.total - s.used
+	use := r.total - r.used
 	if use > len(p) {
 		use = len(p)
 	}
-	copy(p, s.current.data()[s.used:s.used+use])
-	s.used += use
-	if s.used == s.total {
-		if s.delayedErr == nil {
-			if err := s.current.submit(); err == nil {
+	copy(p, r.current.data()[r.used:r.used+use])
+	r.used += use
+	if r.used == r.total {
+		if r.s.err == nil {
+			if err := r.current.submit(); err == nil {
 				// guaranteed to not block, len(transfers) == number of allocated transfers
-				s.transfers <- s.current
+				r.s.transfers <- r.current
 			} else {
-				s.setDelayedErr(err)
+				r.s.gotError(err)
+				r.s.noMore()
 			}
 		}
-		if s.delayedErr != nil {
-			s.current.free()
+		if r.s.err != nil {
+			r.current.free()
 		}
-		s.current = nil
+		r.current = nil
 	}
 	return use, nil
 }
@@ -119,64 +152,112 @@ func (r ReadStream) Read(p []byte) (int, error) {
 // in progress before returning an io.EOF error, unless another error
 // was encountered earlier.
 // Close cannot be called concurrently with Read.
-func (r ReadStream) Close() error {
+func (r *ReadStream) Close() error {
 	if r.s.transfers == nil {
 		return nil
 	}
-	r.s.setDelayedErr(io.EOF)
+	r.s.gotError(io.EOF)
+	r.s.noMore()
 	return nil
 }
 
 // WriteStream is a buffer that will send data asynchronously, reducing
 // the latency between subsequent Write()s.
-/*
 type WriteStream struct {
-	s *stream
+	s     *stream
+	total int
 }
-*/
 
 // Write sends the data to the endpoint. Write returning a nil error doesn't
 // mean that data was written to the device, only that it was written to the
-// buffer. Only a call to Flush() that returns nil error guarantees that
+// buffer. Only a call to Close() that returns nil error guarantees that
 // all transfers have succeeded.
-// TODO(sebek): not implemented and tested yet
-/*
-func (w WriteStream) Write(p []byte) (int, error) {
-	s := w.s
+// If the slice passed to Write does not align exactly with the transfer
+// buffer size (as declared in a call to NewStream), the last USB transfer
+// of this Write will be sent with less data than the full buffer.
+// After a non-nil error is returned, all subsequent attempts to write will
+// return io.ErrClosedPipe.
+// If Write encounters an error when preparing the transfer, the stream
+// will still try to complete any pending transfers. The total number
+// of bytes successfully written can be retrieved through a Written()
+// call after Close() has returned.
+// Write cannot be called concurrently with another Write, Written or Close.
+func (w *WriteStream) Write(p []byte) (int, error) {
+	if w.s.transfers == nil || w.s.err != nil {
+		return 0, io.ErrClosedPipe
+	}
 	written := 0
 	all := len(p)
 	for written < all {
-		if s.current == nil {
-			s.current = <-s.transfers
-			s.total = len(s.current.data())
-			s.used = 0
+		t := <-w.s.transfers
+		n, err := t.wait() // unsubmitted transfers will return 0 bytes and no error
+		w.total += n
+		if err != nil {
+			t.free()
+			w.s.gotError(err)
+			// This branch is used only after all the transfers were set in flight.
+			// That means all transfers left in the queue are in flight.
+			// They must be ignored, since this wait() failed.
+			w.s.flushRemaining()
+			return written, err
 		}
 		use := all - written
-		if use > s.total {
-			use = s.total
+		if max := len(t.data()); use > max {
+			use = max
 		}
-		copy(s.current.data()[s.used:], p[written:written+use])
+		copy(t.data(), p[written:written+use])
+		if err := t.submit(); err != nil {
+			t.free()
+			w.s.gotError(err)
+			// Even though this submit failed, all the transfers in flight are still valid.
+			// Don't flush remaining transfers.
+			// We won't submit any more transfers.
+			w.s.noMore()
+			return written, err
+		}
+		written += use
+		w.s.transfers <- t // guaranteed non blocking
 	}
-	return 0, nil
+	return written, nil
 }
 
-func (w WriteStream) Flush() error {
-	return nil
+// Close signals end of data to write. Close blocks until all transfers
+// that were sent are finished. The error returned by Close is the first
+// error encountered during writing the entire stream (if any).
+// Close returning nil indicates all transfers completed successfuly.
+// After Close, the total number of bytes successfuly written can be
+// retrieved using Written().
+// Close may not be called concurrently with Write, Close or Written.
+func (w *WriteStream) Close() error {
+	if w.s.transfers == nil {
+		return io.ErrClosedPipe
+	}
+	w.s.noMore()
+	for t := range w.s.transfers {
+		n, err := t.wait()
+		w.total += n
+		t.free()
+		if err != nil {
+			w.s.gotError(err)
+			w.s.flushRemaining()
+		}
+		t.free()
+	}
+	w.s.transfers = nil
+	return w.s.err
 }
-*/
 
-func newStream(tt []transferIntf, submit bool) *stream {
+// Written returns the number of bytes successfuly written by the stream.
+// Written may be called only after Close() has been called and returned.
+func (w *WriteStream) Written() int {
+	return w.total
+}
+
+func newStream(tt []transferIntf) *stream {
 	s := &stream{
 		transfers: make(chan transferIntf, len(tt)),
 	}
 	for _, t := range tt {
-		if submit {
-			if err := t.submit(); err != nil {
-				t.free()
-				s.setDelayedErr(err)
-				break
-			}
-		}
 		s.transfers <- t
 	}
 	return s
diff --git a/transfer_stream_test.go b/transfer_stream_test.go
index b159ca8..38614f7 100644
--- a/transfer_stream_test.go
+++ b/transfer_stream_test.go
@@ -62,7 +62,7 @@ func (f *fakeStreamTransfer) wait() (int, error) {
 		return 0, errors.New("wait() called on a free()d transfer")
 	}
 	if !f.inFlight {
-		return 0, errors.New("wait() called without submit()")
+		return 0, nil
 	}
 	if len(f.res) == 0 {
 		return 0, errors.New("wait() called but fake result missing")
@@ -224,7 +224,8 @@ func TestTransferReadStream(t *testing.T) {
 				}
 				tt[i] = ftt[i]
 			}
-			s := ReadStream{newStream(tt, true)}
+			s := ReadStream{s: newStream(tt)}
+			s.s.submitAll()
 			buf := make([]byte, 400)
 			got := make([]readRes, len(tc.want))
 			for i := range tc.want {
@@ -250,3 +251,106 @@ func TestTransferReadStream(t *testing.T) {
 		})
 	}
 }
+
+func TestTransferWriteStream(t *testing.T) {
+	t.Parallel()
+	for _, tc := range []struct {
+		desc      string
+		transfers [][]fakeStreamResult
+		writes    []int
+		want      []int
+		total     int
+		err       error
+	}{
+		{
+			desc: "successful two transfers",
+			transfers: [][]fakeStreamResult{
+				{{n: 1500}},
+				{{n: 1500}},
+				{{n: 1500}},
+			},
+			writes: []int{3000},
+			want:   []int{3000},
+			total:  3000,
+		},
+		{
+			desc: "submit failed on second transfer",
+			transfers: [][]fakeStreamResult{
+				{{n: 1500}},
+				{{submitErr: errSentinel}},
+				{{n: 1500}},
+			},
+			writes: []int{3000},
+			want:   []int{1500},
+			total:  1500,
+			err:    errSentinel,
+		},
+		{
+			desc: "wait failed on second transfer",
+			transfers: [][]fakeStreamResult{
+				{{n: 1500}},
+				{{waitErr: errSentinel}},
+				{{n: 1500}},
+			},
+			writes: []int{3000, 1500},
+			want:   []int{3000, 1500},
+			total:  1500,
+			err:    errSentinel,
+		},
+		{
+			desc: "reused transfer",
+			transfers: [][]fakeStreamResult{
+				{{n: 1500}, {n: 1500}},
+				{{n: 1500}, {n: 1500}},
+				{{n: 1500}, {n: 500}},
+			},
+			writes: []int{3000, 3000, 2000},
+			want:   []int{3000, 3000, 2000},
+			total:  8000,
+		},
+		{
+			desc: "wait failed on reused transfer",
+			transfers: [][]fakeStreamResult{
+				{{n: 1500}, {n: 1500}},
+				{{waitErr: errSentinel}, {n: 1500}},
+				{{n: 1500}, {n: 1500}},
+			},
+			writes: []int{1500, 1500, 1500, 1500, 1500},
+			want:   []int{1500, 1500, 1500, 1500, 0},
+			total:  1500,
+			err:    errSentinel,
+		},
+	} {
+		tc := tc
+		t.Run(tc.desc, func(t *testing.T) {
+			t.Parallel()
+			ftt := make([]*fakeStreamTransfer, len(tc.transfers))
+			tt := make([]transferIntf, len(tc.transfers))
+			for i := range tc.transfers {
+				ftt[i] = &fakeStreamTransfer{
+					res: tc.transfers[i],
+				}
+				tt[i] = ftt[i]
+			}
+			s := WriteStream{s: newStream(tt)}
+			for i, w := range tc.writes {
+				got, err := s.Write(make([]byte, w))
+				if want := tc.want[i]; got != want {
+					t.Errorf("WriteStream.Write #%d: got %d, want %d", i, got, want)
+				}
+				if err != nil && err != tc.err {
+					t.Errorf("WriteStream.Write: got error %v, want %v", err, tc.err)
+				}
+			}
+			if err := s.Close(); err != tc.err {
+				t.Fatalf("WriteStream.Close: got %v, want %v", err, tc.err)
+			}
+			if err := s.Close(); err != io.ErrClosedPipe {
+				t.Fatalf("second WriteStream.Close: got %v, want %v", err, io.ErrClosedPipe)
+			}
+			if got := s.Written(); got != tc.total {
+				t.Fatalf("WriteStream.Written: got %d, want %d", got, tc.total)
+			}
+		})
+	}
+}
diff --git a/transfer_test.go b/transfer_test.go
index 4c8a1de..372a27c 100644
--- a/transfer_test.go
+++ b/transfer_test.go
@@ -99,19 +99,19 @@ func TestTransferProtocol(t *testing.T) {
 	}
 
 	go func() {
-		ft := f.waitForSubmitted()
+		ft := f.waitForSubmitted(nil)
 		ft.length = 5
 		ft.status = TransferCompleted
 		copy(ft.buf, []byte{1, 2, 3, 4, 5})
 		ft.done <- struct{}{}
 
-		ft = f.waitForSubmitted()
+		ft = f.waitForSubmitted(nil)
 		ft.length = 99
 		ft.status = TransferCompleted
 		copy(ft.buf, []byte{12, 12, 12, 12, 12})
 		ft.done <- struct{}{}
 
-		ft = f.waitForSubmitted()
+		ft = f.waitForSubmitted(nil)
 		ft.length = 123
 		ft.status = TransferCancelled
 		ft.done <- struct{}{}