diff --git a/bson/stream.go b/bson/stream.go
new file mode 100644
index 000000000..466528457
--- /dev/null
+++ b/bson/stream.go
@@ -0,0 +1,90 @@
+package bson
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+const (
+	// MinDocumentSize is the size of the smallest possible valid BSON document:
+	// an int32 size header + 0x00 (end of document).
+	MinDocumentSize = 5
+
+	// MaxDocumentSize is the largest possible size for a BSON document allowed by MongoDB,
+	// that is, 16 MiB (see https://docs.mongodb.com/manual/reference/limits/).
+	MaxDocumentSize = 16777216
+)
+
+// ErrInvalidDocumentSize is an error returned when a BSON document's header
+// contains a size smaller than MinDocumentSize or greater than MaxDocumentSize.
+type ErrInvalidDocumentSize struct {
+	DocumentSize int32
+}
+
+func (e ErrInvalidDocumentSize) Error() string {
+	return fmt.Sprintf("invalid document size %d", e.DocumentSize)
+}
+
+// A Decoder reads and decodes BSON values from an input stream.
+type Decoder struct {
+	source io.Reader
+}
+
+// NewDecoder returns a new Decoder that reads from source.
+// It does not add any extra buffering, and may not read data from source beyond the BSON values requested.
+func NewDecoder(source io.Reader) *Decoder {
+	return &Decoder{source: source}
+}
+
+// Decode reads the next BSON-encoded value from its input and stores it in the value pointed to by v.
+// See the documentation for Unmarshal for details about the conversion of BSON into a Go value.
+func (dec *Decoder) Decode(v interface{}) (err error) {
+	// BSON documents start with their size as a *signed* int32.
+	var docSize int32
+	if err = binary.Read(dec.source, binary.LittleEndian, &docSize); err != nil {
+		return
+	}
+
+	if docSize < MinDocumentSize || docSize > MaxDocumentSize {
+		return ErrInvalidDocumentSize{DocumentSize: docSize}
+	}
+
+	docBuffer := bytes.NewBuffer(make([]byte, 0, docSize))
+	if err = binary.Write(docBuffer, binary.LittleEndian, docSize); err != nil {
+		return
+	}
+
+	// docSize is the *full* document's size (including the 4-byte size header,
+	// which has already been read).
+	if _, err = io.CopyN(docBuffer, dec.source, int64(docSize-4)); err != nil {
+		return
+	}
+
+	// Let Unmarshal handle the rest.
+	defer handleErr(&err)
+	return Unmarshal(docBuffer.Bytes(), v)
+}
+
+// An Encoder encodes and writes BSON values to an output stream.
+type Encoder struct {
+	target io.Writer
+}
+
+// NewEncoder returns a new Encoder that writes to target.
+func NewEncoder(target io.Writer) *Encoder {
+	return &Encoder{target: target}
+}
+
+// Encode encodes v to BSON, and if successful writes it to the Encoder's output stream.
+// See the documentation for Marshal for details about the conversion of Go values to BSON.
+func (enc *Encoder) Encode(v interface{}) error {
+	data, err := Marshal(v)
+	if err != nil {
+		return err
+	}
+
+	_, err = enc.target.Write(data)
+	return err
+}
diff --git a/bson/stream_test.go b/bson/stream_test.go
new file mode 100644
index 000000000..14acbe3c5
--- /dev/null
+++ b/bson/stream_test.go
@@ -0,0 +1,77 @@
+package bson_test
+
+import (
+	"bytes"
+
+	"github.com/globalsign/mgo/bson"
+	. "gopkg.in/check.v1"
+)
+
+var invalidSizeDocuments = [][]byte{
+	// Empty document
+	[]byte{},
+	// Incomplete header
+	[]byte{0x04},
+	// Negative size
+	[]byte{0xff, 0xff, 0xff, 0xff},
+	// Full, valid size header but too small (less than 5 bytes)
+	[]byte{0x04, 0x00, 0x00, 0x00},
+	// Valid header, valid size but incomplete document
+	[]byte{0xff, 0x00, 0x00, 0x00, 0x00},
+	// Too big
+	[]byte{0xff, 0xff, 0xff, 0x7f},
+}
+
+// Reusing sampleItems from bson_test
+
+func (s *S) TestEncodeSampleItems(c *C) {
+	for i, item := range sampleItems {
+		buf := bytes.NewBuffer(nil)
+		enc := bson.NewEncoder(buf)
+
+		err := enc.Encode(item.obj)
+		c.Assert(err, IsNil)
+		c.Assert(string(buf.Bytes()), Equals, item.data, Commentf("Failed on item %d", i))
+	}
+}
+
+func (s *S) TestDecodeSampleItems(c *C) {
+	for i, item := range sampleItems {
+		buf := bytes.NewBuffer([]byte(item.data))
+		dec := bson.NewDecoder(buf)
+
+		value := bson.M{}
+		err := dec.Decode(&value)
+		c.Assert(err, IsNil)
+		c.Assert(value, DeepEquals, item.obj, Commentf("Failed on item %d", i))
+	}
+}
+
+func (s *S) TestStreamRoundTrip(c *C) {
+	buf := bytes.NewBuffer(nil)
+	enc := bson.NewEncoder(buf)
+
+	for _, item := range sampleItems {
+		err := enc.Encode(item.obj)
+		c.Assert(err, IsNil)
+	}
+
+	// Ensure that everything that was encoded is decodable in the same order.
+	dec := bson.NewDecoder(buf)
+	for i, item := range sampleItems {
+		value := bson.M{}
+		err := dec.Decode(&value)
+		c.Assert(err, IsNil)
+		c.Assert(value, DeepEquals, item.obj, Commentf("Failed on item %d", i))
+	}
+}
+
+func (s *S) TestDecodeDocumentTooSmall(c *C) {
+	for i, item := range invalidSizeDocuments {
+		buf := bytes.NewBuffer(item)
+		dec := bson.NewDecoder(buf)
+		value := bson.M{}
+		err := dec.Decode(&value)
+		c.Assert(err, NotNil, Commentf("Failed on invalid size item %d", i))
+	}
+}