diff --git a/peer.go b/peer.go
index c08ea32..9ab851c 100644
--- a/peer.go
+++ b/peer.go
@@ -2,6 +2,12 @@ package enet
 
 // #include <enet/enet.h>
 import "C"
+import (
+	"encoding/binary"
+	"fmt"
+	"math"
+	"unsafe"
+)
 
 // Peer is a peer which data packets may be sent or received from
 type Peer interface {
@@ -14,6 +20,25 @@ type Peer interface {
 	SendBytes(data []byte, channel uint8, flags PacketFlags) error
 	SendString(str string, channel uint8, flags PacketFlags) error
 	SendPacket(packet Packet, channel uint8) error
+
+	// SetData sets an arbitrary value against a peer. This is useful to attach some
+	// application-specific data for future use, such as an identifier.
+	//
+	// http://enet.bespin.org/structENetPeer.html#a1873959810db7ac7a02da90469ee384e
+	//
+	// Note that due to the way the enet library works, if using this you are
+	// responsible for clearing this data when the peer is finished with.
+	// SetData(nil) will free underlying memory and avoid any leaks.
+	//
+	// See http://enet.bespin.org/Tutorial.html#ManageHost for an example of this
+	// in the underlying library.
+	SetData(data []byte)
+
+	// GetData returns an application-specific value that's been set
+	// against this peer. This returns nil if no data has been set.
+	//
+	// http://enet.bespin.org/structENetPeer.html#a1873959810db7ac7a02da90469ee384e
+	GetData() []byte
 }
 
 type enetPeer struct {
@@ -71,3 +96,53 @@ func (peer enetPeer) SendPacket(packet Packet, channel uint8) error {
 	)
 	return nil
 }
+
+func (peer enetPeer) SetData(data []byte) {
+	if len(data) > math.MaxUint32 {
+		panic(fmt.Sprintf("maximum peer data length is uint32 (%d)", math.MaxUint32))
+	}
+
+	// Free any data that was previously stored against this peer.
+	existing := unsafe.Pointer(peer.cPeer.data)
+	if existing != nil {
+		C.free(existing)
+	}
+
+	// If nil, set this explicitly.
+	if data == nil {
+		peer.cPeer.data = nil
+		return
+	}
+
+	// First 4 bytes stores how many bytes we have. This is so we can C.GoBytes when
+	// retrieving which requires a byte length to read.
+	b := make([]byte, len(data)+4)
+	binary.LittleEndian.PutUint32(b, uint32(len(data)))
+	// Join this header + data in to a contiguous slice
+	copy(b[4:], data)
+	// And write it out to C memory, storing our pointer.
+	peer.cPeer.data = unsafe.Pointer(C.CBytes(b))
+}
+
+func (peer enetPeer) GetData() []byte {
+	ptr := unsafe.Pointer(peer.cPeer.data)
+
+	if ptr == nil {
+		return nil
+	}
+
+	// First 4 bytes are the bytes length.
+	header := []byte{
+		*(*byte)(unsafe.Add(ptr, 0)),
+		*(*byte)(unsafe.Add(ptr, 1)),
+		*(*byte)(unsafe.Add(ptr, 2)),
+		*(*byte)(unsafe.Add(ptr, 3)),
+	}
+
+	return []byte(C.GoBytes(
+		// Take from the start of the data.
+		unsafe.Add(ptr, 4),
+		// As many bytes as were indicated in the header.
+		C.int(binary.LittleEndian.Uint32(header)),
+	))
+}
diff --git a/peer_test.go b/peer_test.go
new file mode 100644
index 0000000..a4daebd
--- /dev/null
+++ b/peer_test.go
@@ -0,0 +1,209 @@
+package enet_test
+
+import (
+	"fmt"
+	"github.com/codecat/go-enet"
+	"os"
+	"os/exec"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestPeerData(t *testing.T) {
+	testData := []byte{0x1, 0x2, 0x3}
+
+	// peer is connected to our server.
+	// events will produce events as the server receives them.
+	peer, events := createServerClient(t)
+
+	// Wait for the server to respond with a connection.
+	ev := <-events
+	if data := ev.GetPeer().GetData(); data != nil {
+		t.Fatalf("did not expect new peer to have data set, but has %x", data)
+	}
+
+	// Set some data against our peer and immediately check it's there.
+	ev.GetPeer().SetData(testData)
+	assertPeerData(t, ev.GetPeer(), testData, "immediate after set")
+
+	// Send a message to the server.
+	if err := peer.SendString("testmessage", 0, enet.PacketFlagReliable); err != nil {
+		t.Fatal(err)
+	}
+
+	// Wait for the server to receive this message, then check the
+	// server-side peer associated with this event has the data
+	// we set previously.
+	ev = <-events
+	assertPeerData(t, ev.GetPeer(), testData, "on packet received")
+
+	t.Run("clear-data", func(t *testing.T) {
+		ev.GetPeer().SetData(nil)
+		assertPeerData(t, ev.GetPeer(), nil, "nil set")
+	})
+
+	t.Run("empty-slice", func(t *testing.T) {
+		ev.GetPeer().SetData([]byte{})
+		assertPeerData(t, ev.GetPeer(), []byte{}, "empty set")
+	})
+
+	// Check that our data stored in C survives garbage collection.
+	t.Run("survives-gc", func(t *testing.T) {
+		ev.GetPeer().SetData([]byte{1, 2, 3})
+		runtime.GC()
+		assertPeerData(t, ev.GetPeer(), []byte{1, 2, 3}, "after GC")
+	})
+
+	// Sniffs for a potential memory leak in our set data implementation.
+	// We expect SetData to clear whatever C memory was used previously.
+	// This may end up being a flaky test, but will keep it in for now to
+	// build confidence in our implementation.
+	t.Run("memory-leaks", func(t *testing.T) {
+		if runtime.GOOS != "linux" {
+			t.Skipf("skipping mem leak test as not running on a linux host")
+		}
+
+		noOfIncreases := 0
+		last := currentMemory(t)
+
+		// Assign a large string (10MB) to data over and over again, checking
+		// for continuous increases in mem usage, with some threshold.
+		for i := 0; i < 99; i++ {
+			ev.GetPeer().SetData([]byte(strings.Repeat("x", 1024*1024*10)))
+
+			// Detect a memory leak by checking if we're using more than 1MB last than the
+			// previous for too many iterations.
+			now := currentMemory(t)
+
+			if now-last > 1024 {
+				noOfIncreases++
+			} else {
+				// If it's not an increase, reset our counter.
+				noOfIncreases = 0
+			}
+
+			// If we reach a threshold of 5 continuous increases, consider this a leak.
+			if noOfIncreases > 5 {
+				t.Fatal("potential memory leak detected")
+			}
+
+			last = now
+		}
+	})
+}
+
+func assertPeerData(t testing.TB, peer enet.Peer, expected []byte, msg string) {
+	t.Helper()
+
+	actual := peer.GetData()
+
+	if (actual == nil) != (expected == nil) {
+		t.Fatalf("%s: expected peer data to be present? %t vs actual: %t", msg, expected != nil, actual != nil)
+	}
+
+	if len(actual) != len(expected) {
+		t.Fatalf("%s: expected peer data to have len %d vs actual %d", msg, len(expected), len(actual))
+	}
+
+	if string(actual) != string(expected) {
+		t.Fatalf("%s: expected peer data to be %v, but it was %v", msg, expected, actual)
+	}
+}
+
+// createServerClient creates a dummy enet server and client. The returned
+// peer can be used to send messages to the server, and the blocking events
+// channel returned will be given each event as the server picks it up.
+func createServerClient(t *testing.T) (clientConn enet.Peer, serverEvents <-chan enet.Event) {
+	port := getFreePort()
+
+	done := make(chan bool, 0)
+	events := make(chan enet.Event)
+
+	t.Cleanup(func() {
+		// Kill our background service routines for client & server.
+		close(done)
+	})
+
+	// Create a server and continuously service it, exposing any captured events.
+	server, err := enet.NewHost(enet.NewListenAddress(port), 10, 1, 0, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	go func() {
+		for true {
+			select {
+			case <-done:
+				return
+			default:
+				ev := server.Service(0)
+
+				// Pass any event out to our channel. This will block
+				// until a test consumes it.
+				if ev.GetType() != enet.EventNone {
+					events <- ev
+				}
+			}
+		}
+	}()
+
+	// Create a client and continuously service it in the background.
+	client, err := enet.NewHost(nil, 1, 1, 0, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	go func() {
+		for true {
+			select {
+			case <-done:
+				return
+			default:
+				client.Service(0)
+			}
+		}
+	}()
+
+	// Connect to our server.
+	peer, err := client.Connect(enet.NewAddress("localhost", port), 1, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return peer, events
+}
+
+var port uint16 = 49152
+
+// getFreePort returns a unique private port. Note this doesn't guarantee
+// it's free, but should be good enough from within docker tests.
+func getFreePort() uint16 {
+	port++
+	return port
+}
+
+// currentMemory returns the memory usage of the current process according to
+// the OS. This uses linux's proc FS to give a rough estimate based on VmSize.
+// Note we don't want to use runtime.MemStats here as we're looking for the
+// total memory (including C allocations).
+func currentMemory(t testing.TB) int {
+	// GC to give a stable measure.
+	runtime.GC()
+
+	pmapCmd := fmt.Sprintf("pmap %d | grep total | grep -Eo '[0-9]+'", os.Getpid())
+	cmd := exec.Command("bash", "-c", pmapCmd)
+
+	output, err := cmd.Output()
+	if err != nil {
+		t.Fatalf("failed to run memory check command: %s", err)
+	}
+
+	kb, err := strconv.Atoi(strings.TrimSpace(string(output)))
+	if err != nil {
+		t.Fatalf("failed converting memory output provided by pmap to int: %s", err)
+	}
+
+	return kb
+}