diff --git a/comm.go b/comm.go
index 430e6a6..182e992 100644
--- a/comm.go
+++ b/comm.go
@@ -104,3 +104,21 @@ func rpcWithSubs(subs ...*pb.RPC_SubOpts) *RPC {
 func rpcWithMessages(msgs ...*pb.Message) *RPC {
 	return &RPC{RPC: pb.RPC{Publish: msgs}}
 }
+
+func rpcWithControl(msgs []*pb.Message,
+	ihave []*pb.ControlIHave,
+	iwant []*pb.ControlIWant,
+	graft []*pb.ControlGraft,
+	prune []*pb.ControlPrune) *RPC {
+	return &RPC{
+		RPC: pb.RPC{
+			Publish: msgs,
+			Control: &pb.ControlMessage{
+				Ihave: ihave,
+				Iwant: iwant,
+				Graft: graft,
+				Prune: prune,
+			},
+		},
+	}
+}
diff --git a/floodsub.go b/floodsub.go
index 65d640a..1b2eb08 100644
--- a/floodsub.go
+++ b/floodsub.go
@@ -78,3 +78,7 @@ func (fs *FloodSubRouter) Publish(from peer.ID, msg *pb.Message) {
 		}
 	}
 }
+
+func (fs *FloodSubRouter) Join(topic string) {}
+
+func (fs *FloodSubRouter) Leave(topic string) {}
diff --git a/floodsub_test.go b/floodsub_test.go
index e7b421f..b0196ca 100644
--- a/floodsub_test.go
+++ b/floodsub_test.go
@@ -55,8 +55,16 @@ func connect(t *testing.T, a, b host.Host) {
 }
 
 func sparseConnect(t *testing.T, hosts []host.Host) {
+	connectSome(t, hosts, 3)
+}
+
+func denseConnect(t *testing.T, hosts []host.Host) {
+	connectSome(t, hosts, 10)
+}
+
+func connectSome(t *testing.T, hosts []host.Host, d int) {
 	for i, a := range hosts {
-		for j := 0; j < 3; j++ {
+		for j := 0; j < d; j++ {
 			n := rand.Intn(len(hosts))
 			if n == i {
 				j--
diff --git a/gossipsub.go b/gossipsub.go
new file mode 100644
index 0000000..2648530
--- /dev/null
+++ b/gossipsub.go
@@ -0,0 +1,613 @@
+package floodsub
+
+import (
+	"context"
+	"math/rand"
+	"time"
+
+	pb "github.com/libp2p/go-floodsub/pb"
+
+	host "github.com/libp2p/go-libp2p-host"
+	peer "github.com/libp2p/go-libp2p-peer"
+	protocol "github.com/libp2p/go-libp2p-protocol"
+)
+
+const (
+	GossipSubID = protocol.ID("/meshsub/1.0.0")
+)
+
+var (
+	// overlay parameters
+	GossipSubD   = 6
+	GossipSubDlo = 4
+	GossipSubDhi = 12
+
+	// gossip parameters
+	GossipSubHistoryLength = 5
+	GossipSubHistoryGossip = 3
+
+	// heartbeat interval
+	GossipSubHeartbeatInterval = 1 * time.Second
+
+	// fanout ttl
+	GossipSubFanoutTTL = 60 * time.Second
+)
+
+// NewGossipSub returns a new PubSub object using GossipSubRouter as the router
+func NewGossipSub(ctx context.Context, h host.Host, opts ...Option) (*PubSub, error) {
+	rt := &GossipSubRouter{
+		peers:   make(map[peer.ID]protocol.ID),
+		mesh:    make(map[string]map[peer.ID]struct{}),
+		fanout:  make(map[string]map[peer.ID]struct{}),
+		lastpub: make(map[string]int64),
+		gossip:  make(map[peer.ID][]*pb.ControlIHave),
+		control: make(map[peer.ID]*pb.ControlMessage),
+		mcache:  NewMessageCache(GossipSubHistoryGossip, GossipSubHistoryLength),
+	}
+	return NewPubSub(ctx, h, rt, opts...)
+}
+
+// GossipSubRouter is a router that implements the gossipsub protocol.
+// For each topic we have joined, we maintain an overlay through which
+// messages flow; this is the mesh map.
+// For each topic we publish to without joining, we maintain a list of peers
+// to use for injecting our messages in the overlay with stable routes; this
+// is the fanout map. Fanout peer lists are expired if we don't publish any
+// messages to their topic for GossipSubFanoutTTL.
+type GossipSubRouter struct {
+	p       *PubSub
+	peers   map[peer.ID]protocol.ID         // peer protocols
+	mesh    map[string]map[peer.ID]struct{} // topic meshes
+	fanout  map[string]map[peer.ID]struct{} // topic fanout
+	lastpub map[string]int64                // last pubish time for fanout topics
+	gossip  map[peer.ID][]*pb.ControlIHave  // pending gossip
+	control map[peer.ID]*pb.ControlMessage  // pending control messages
+	mcache  *MessageCache
+}
+
+func (gs *GossipSubRouter) Protocols() []protocol.ID {
+	return []protocol.ID{GossipSubID, FloodSubID}
+}
+
+func (gs *GossipSubRouter) Attach(p *PubSub) {
+	gs.p = p
+	go gs.heartbeatTimer()
+}
+
+func (gs *GossipSubRouter) AddPeer(p peer.ID, proto protocol.ID) {
+	gs.peers[p] = proto
+}
+
+func (gs *GossipSubRouter) RemovePeer(p peer.ID) {
+	delete(gs.peers, p)
+	for _, peers := range gs.mesh {
+		delete(peers, p)
+	}
+	for _, peers := range gs.fanout {
+		delete(peers, p)
+	}
+	delete(gs.gossip, p)
+	delete(gs.control, p)
+}
+
+func (gs *GossipSubRouter) HandleRPC(rpc *RPC) {
+	ctl := rpc.GetControl()
+	if ctl == nil {
+		return
+	}
+
+	iwant := gs.handleIHave(ctl)
+	ihave := gs.handleIWant(ctl)
+	prune := gs.handleGraft(rpc.from, ctl)
+	gs.handlePrune(rpc.from, ctl)
+
+	if len(iwant) == 0 && len(ihave) == 0 && len(prune) == 0 {
+		return
+	}
+
+	out := rpcWithControl(ihave, nil, iwant, nil, prune)
+	gs.sendRPC(rpc.from, out)
+}
+
+func (gs *GossipSubRouter) handleIHave(ctl *pb.ControlMessage) []*pb.ControlIWant {
+	iwant := make(map[string]struct{})
+
+	for _, ihave := range ctl.GetIhave() {
+		topic := ihave.GetTopicID()
+		_, ok := gs.mesh[topic]
+		if !ok {
+			continue
+		}
+
+		for _, mid := range ihave.GetMessageIDs() {
+			if gs.p.seenMessage(mid) {
+				continue
+			}
+			iwant[mid] = struct{}{}
+		}
+	}
+
+	if len(iwant) == 0 {
+		return nil
+	}
+
+	iwantlst := make([]string, 0, len(iwant))
+	for mid := range iwant {
+		iwantlst = append(iwantlst, mid)
+	}
+
+	return []*pb.ControlIWant{&pb.ControlIWant{MessageIDs: iwantlst}}
+}
+
+func (gs *GossipSubRouter) handleIWant(ctl *pb.ControlMessage) []*pb.Message {
+	ihave := make(map[string]*pb.Message)
+	for _, iwant := range ctl.GetIwant() {
+		for _, mid := range iwant.GetMessageIDs() {
+			msg, ok := gs.mcache.Get(mid)
+			if ok {
+				ihave[mid] = msg
+			}
+		}
+	}
+
+	if len(ihave) == 0 {
+		return nil
+	}
+
+	msgs := make([]*pb.Message, 0, len(ihave))
+	for _, msg := range ihave {
+		msgs = append(msgs, msg)
+	}
+
+	return msgs
+}
+
+func (gs *GossipSubRouter) handleGraft(p peer.ID, ctl *pb.ControlMessage) []*pb.ControlPrune {
+	var prune []string
+	for _, graft := range ctl.GetGraft() {
+		topic := graft.GetTopicID()
+		peers, ok := gs.mesh[topic]
+		if !ok {
+			prune = append(prune, topic)
+		} else {
+			peers[p] = struct{}{}
+		}
+	}
+
+	if len(prune) == 0 {
+		return nil
+	}
+
+	cprune := make([]*pb.ControlPrune, 0, len(prune))
+	for _, topic := range prune {
+		cprune = append(cprune, &pb.ControlPrune{TopicID: &topic})
+	}
+
+	return cprune
+}
+
+func (gs *GossipSubRouter) handlePrune(p peer.ID, ctl *pb.ControlMessage) {
+	for _, prune := range ctl.GetPrune() {
+		topic := prune.GetTopicID()
+		peers, ok := gs.mesh[topic]
+		if ok {
+			delete(peers, p)
+		}
+	}
+}
+
+func (gs *GossipSubRouter) Publish(from peer.ID, msg *pb.Message) {
+	gs.mcache.Put(msg)
+
+	tosend := make(map[peer.ID]struct{})
+	for _, topic := range msg.GetTopicIDs() {
+		// any peers in the topic?
+		tmap, ok := gs.p.topics[topic]
+		if !ok {
+			continue
+		}
+
+		// floodsub peers
+		for p := range tmap {
+			if gs.peers[p] == FloodSubID {
+				tosend[p] = struct{}{}
+			}
+		}
+
+		// gossipsub peers
+		gmap, ok := gs.mesh[topic]
+		if !ok {
+			// we are not in the mesh for topic, use fanout peers
+			gmap, ok = gs.fanout[topic]
+			if !ok {
+				// we don't have any, pick some
+				peers := gs.getPeers(topic, GossipSubD, func(peer.ID) bool { return true })
+
+				if len(peers) > 0 {
+					gmap = peerListToMap(peers)
+					gs.fanout[topic] = gmap
+				}
+			}
+			gs.lastpub[topic] = time.Now().UnixNano()
+		}
+
+		for p := range gmap {
+			tosend[p] = struct{}{}
+		}
+	}
+
+	out := rpcWithMessages(msg)
+	for pid := range tosend {
+		if pid == from || pid == peer.ID(msg.GetFrom()) {
+			continue
+		}
+
+		gs.sendRPC(pid, out)
+	}
+}
+
+func (gs *GossipSubRouter) Join(topic string) {
+	gmap, ok := gs.mesh[topic]
+	if ok {
+		return
+	}
+
+	gmap, ok = gs.fanout[topic]
+	if ok {
+		gs.mesh[topic] = gmap
+		delete(gs.fanout, topic)
+		delete(gs.lastpub, topic)
+	} else {
+		peers := gs.getPeers(topic, GossipSubD, func(peer.ID) bool { return true })
+		gmap = peerListToMap(peers)
+		gs.mesh[topic] = gmap
+	}
+
+	for p := range gmap {
+		gs.sendGraft(p, topic)
+	}
+}
+
+func (gs *GossipSubRouter) Leave(topic string) {
+	gmap, ok := gs.mesh[topic]
+	if !ok {
+		return
+	}
+
+	delete(gs.mesh, topic)
+
+	for p := range gmap {
+		gs.sendPrune(p, topic)
+	}
+}
+
+func (gs *GossipSubRouter) sendGraft(p peer.ID, topic string) {
+	graft := []*pb.ControlGraft{&pb.ControlGraft{TopicID: &topic}}
+	out := rpcWithControl(nil, nil, nil, graft, nil)
+	gs.sendRPC(p, out)
+}
+
+func (gs *GossipSubRouter) sendPrune(p peer.ID, topic string) {
+	prune := []*pb.ControlPrune{&pb.ControlPrune{TopicID: &topic}}
+	out := rpcWithControl(nil, nil, nil, nil, prune)
+	gs.sendRPC(p, out)
+}
+
+func (gs *GossipSubRouter) sendRPC(p peer.ID, out *RPC) {
+	// piggyback cotrol message retries
+	ctl, ok := gs.control[p]
+	if ok {
+		gs.piggybackControl(p, out, ctl)
+		delete(gs.control, p)
+	}
+
+	// piggyback gossip
+	ihave, ok := gs.gossip[p]
+	if ok {
+		gs.piggybackGossip(p, out, ihave)
+		delete(gs.gossip, p)
+	}
+
+	mch, ok := gs.p.peers[p]
+	if !ok {
+		return
+	}
+
+	select {
+	case mch <- out:
+	default:
+		log.Infof("dropping message to peer %s: queue full", p)
+		// push control messages that need to be retried
+		ctl := out.GetControl()
+		if ctl != nil {
+			gs.pushControl(p, ctl)
+		}
+	}
+}
+
+func (gs *GossipSubRouter) heartbeatTimer() {
+	ticker := time.NewTicker(GossipSubHeartbeatInterval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			select {
+			case gs.p.eval <- gs.heartbeat:
+			case <-gs.p.ctx.Done():
+				return
+			}
+		case <-gs.p.ctx.Done():
+			return
+		}
+	}
+}
+
+func (gs *GossipSubRouter) heartbeat() {
+	// flush pending control message from retries and gossip
+	// that hasn't been piggybacked since the last heartbeat
+	gs.flush()
+
+	tograft := make(map[peer.ID][]string)
+	toprune := make(map[peer.ID][]string)
+
+	// maintain the mesh for topics we have joined
+	for topic, peers := range gs.mesh {
+
+		// do we have enough peers?
+		if len(peers) < GossipSubDlo {
+			ineed := GossipSubD - len(peers)
+			plst := gs.getPeers(topic, ineed, func(p peer.ID) bool {
+				// filter our current peers
+				_, ok := peers[p]
+				return !ok
+			})
+
+			for _, p := range plst {
+				peers[p] = struct{}{}
+				topics := tograft[p]
+				tograft[p] = append(topics, topic)
+			}
+		}
+
+		// do we have too many peers?
+		if len(peers) > GossipSubDhi {
+			idontneed := len(peers) - GossipSubD
+			plst := peerMapToList(peers)
+			shufflePeers(plst)
+
+			for _, p := range plst[:idontneed] {
+				delete(peers, p)
+				topics := toprune[p]
+				toprune[p] = append(topics, topic)
+			}
+		}
+
+		gs.emitGossip(topic, peers)
+	}
+
+	// expire fanout for topics we haven't published to in a while
+	now := time.Now().UnixNano()
+	for topic, lastpub := range gs.lastpub {
+		if lastpub+int64(GossipSubFanoutTTL) < now {
+			delete(gs.fanout, topic)
+			delete(gs.lastpub, topic)
+		}
+	}
+
+	// maintain our fanout for topics we are publishing but we have not joined
+	for topic, peers := range gs.fanout {
+		// check whether our peers are still in the topic
+		for p := range peers {
+			_, ok := gs.p.topics[topic][p]
+			if !ok {
+				delete(peers, p)
+			}
+		}
+
+		// do we need more peers?
+		if len(peers) < GossipSubD {
+			ineed := GossipSubD - len(peers)
+			plst := gs.getPeers(topic, ineed, func(p peer.ID) bool {
+				// filter our current peers
+				_, ok := peers[p]
+				return !ok
+			})
+
+			for _, p := range plst {
+				peers[p] = struct{}{}
+			}
+		}
+
+		gs.emitGossip(topic, peers)
+	}
+
+	// send coalesced GRAFT/PRUNE messages (will piggyback gossip)
+	gs.sendGraftPrune(tograft, toprune)
+
+	// advance the message history window
+	gs.mcache.Shift()
+}
+
+func (gs *GossipSubRouter) sendGraftPrune(tograft, toprune map[peer.ID][]string) {
+	for p, topics := range tograft {
+		graft := make([]*pb.ControlGraft, 0, len(topics))
+		for _, topic := range topics {
+			graft = append(graft, &pb.ControlGraft{TopicID: &topic})
+		}
+
+		var prune []*pb.ControlPrune
+		pruning, ok := toprune[p]
+		if ok {
+			delete(toprune, p)
+			prune = make([]*pb.ControlPrune, 0, len(pruning))
+			for _, topic := range pruning {
+				prune = append(prune, &pb.ControlPrune{TopicID: &topic})
+			}
+		}
+
+		out := rpcWithControl(nil, nil, nil, graft, prune)
+		gs.sendRPC(p, out)
+	}
+
+	for p, topics := range toprune {
+		prune := make([]*pb.ControlPrune, 0, len(topics))
+		for _, topic := range topics {
+			prune = append(prune, &pb.ControlPrune{TopicID: &topic})
+		}
+
+		out := rpcWithControl(nil, nil, nil, nil, prune)
+		gs.sendRPC(p, out)
+	}
+
+}
+
+func (gs *GossipSubRouter) emitGossip(topic string, peers map[peer.ID]struct{}) {
+	mids := gs.mcache.GetGossipIDs(topic)
+	if len(mids) == 0 {
+		return
+	}
+
+	gpeers := gs.getPeers(topic, GossipSubD, func(peer.ID) bool { return true })
+	for _, p := range gpeers {
+		// skip mesh peers
+		_, ok := peers[p]
+		if !ok {
+			gs.pushGossip(p, &pb.ControlIHave{TopicID: &topic, MessageIDs: mids})
+		}
+	}
+}
+
+func (gs *GossipSubRouter) flush() {
+	// send gossip first, which will also piggyback control
+	for p, ihave := range gs.gossip {
+		delete(gs.gossip, p)
+		out := rpcWithControl(nil, ihave, nil, nil, nil)
+		gs.sendRPC(p, out)
+	}
+
+	// send the remaining control messages
+	for p, ctl := range gs.control {
+		delete(gs.control, p)
+		out := rpcWithControl(nil, nil, nil, ctl.Graft, ctl.Prune)
+		gs.sendRPC(p, out)
+	}
+}
+
+func (gs *GossipSubRouter) pushGossip(p peer.ID, ihave *pb.ControlIHave) {
+	gossip := gs.gossip[p]
+	gossip = append(gossip, ihave)
+	gs.gossip[p] = gossip
+}
+
+func (gs *GossipSubRouter) piggybackGossip(p peer.ID, out *RPC, ihave []*pb.ControlIHave) {
+	ctl := out.GetControl()
+	if ctl == nil {
+		ctl = &pb.ControlMessage{}
+		out.Control = ctl
+	}
+
+	ctl.Ihave = ihave
+}
+
+func (gs *GossipSubRouter) pushControl(p peer.ID, ctl *pb.ControlMessage) {
+	// remove IHAVE/IWANT from control message, gossip is not retried
+	ctl.Ihave = nil
+	ctl.Iwant = nil
+	if ctl.Graft != nil || ctl.Prune != nil {
+		gs.control[p] = ctl
+	}
+}
+
+func (gs *GossipSubRouter) piggybackControl(p peer.ID, out *RPC, ctl *pb.ControlMessage) {
+	// check control message for staleness first
+	var tograft []*pb.ControlGraft
+	var toprune []*pb.ControlPrune
+
+	for _, graft := range ctl.GetGraft() {
+		topic := graft.GetTopicID()
+		peers, ok := gs.mesh[topic]
+		if !ok {
+			continue
+		}
+		_, ok = peers[p]
+		if ok {
+			tograft = append(tograft, graft)
+		}
+	}
+
+	for _, prune := range ctl.GetPrune() {
+		topic := prune.GetTopicID()
+		peers, ok := gs.mesh[topic]
+		if !ok {
+			toprune = append(toprune, prune)
+			continue
+		}
+		_, ok = peers[p]
+		if !ok {
+			toprune = append(toprune, prune)
+		}
+	}
+
+	if len(tograft) == 0 && len(toprune) == 0 {
+		return
+	}
+
+	xctl := out.Control
+	if xctl == nil {
+		xctl = &pb.ControlMessage{}
+		out.Control = xctl
+	}
+
+	if len(tograft) > 0 {
+		xctl.Graft = append(xctl.Graft, tograft...)
+	}
+	if len(toprune) > 0 {
+		xctl.Prune = append(xctl.Prune, toprune...)
+	}
+}
+
+func (gs *GossipSubRouter) getPeers(topic string, count int, filter func(peer.ID) bool) []peer.ID {
+	tmap, ok := gs.p.topics[topic]
+	if !ok {
+		return nil
+	}
+
+	peers := make([]peer.ID, 0, len(tmap))
+	for p := range tmap {
+		if gs.peers[p] == GossipSubID && filter(p) {
+			peers = append(peers, p)
+		}
+	}
+
+	shufflePeers(peers)
+
+	if count > 0 && len(peers) > count {
+		peers = peers[:count]
+	}
+
+	return peers
+}
+
+func peerListToMap(peers []peer.ID) map[peer.ID]struct{} {
+	pmap := make(map[peer.ID]struct{})
+	for _, p := range peers {
+		pmap[p] = struct{}{}
+	}
+	return pmap
+}
+
+func peerMapToList(peers map[peer.ID]struct{}) []peer.ID {
+	plst := make([]peer.ID, 0, len(peers))
+	for p := range peers {
+		plst = append(plst, p)
+	}
+	return plst
+}
+
+func shufflePeers(peers []peer.ID) {
+	for i := range peers {
+		j := rand.Intn(i + 1)
+		peers[i], peers[j] = peers[j], peers[i]
+	}
+}
diff --git a/gossipsub_test.go b/gossipsub_test.go
new file mode 100644
index 0000000..8dae7ff
--- /dev/null
+++ b/gossipsub_test.go
@@ -0,0 +1,912 @@
+package floodsub
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"math/rand"
+	"testing"
+	"time"
+
+	host "github.com/libp2p/go-libp2p-host"
+)
+
+func getGossipsubs(ctx context.Context, hs []host.Host, opts ...Option) []*PubSub {
+	var psubs []*PubSub
+	for _, h := range hs {
+		ps, err := NewGossipSub(ctx, h, opts...)
+		if err != nil {
+			panic(err)
+		}
+		psubs = append(psubs, ps)
+	}
+	return psubs
+}
+
+func TestSparseGossipsub(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	sparseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestDenseGossipsub(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubFanout(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs[1:] {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := 0
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+
+	// subscribe the owner
+	subch, err := psubs[0].Subscribe("foobar")
+	if err != nil {
+		t.Fatal(err)
+	}
+	msgs = append(msgs, subch)
+
+	// wait for a heartbeat
+	time.Sleep(time.Second * 1)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := 0
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubFanoutMaintenance(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs[1:] {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := 0
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+
+	// unsubscribe all peers to exercise fanout maintenance
+	for _, sub := range msgs {
+		sub.Cancel()
+	}
+	msgs = nil
+
+	// wait for heartbeats
+	time.Sleep(time.Second * 2)
+
+	// resubscribe and repeat
+	for _, ps := range psubs[1:] {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := 0
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubFanoutExpiry(t *testing.T) {
+	GossipSubFanoutTTL = 1 * time.Second
+	defer func() { GossipSubFanoutTTL = 60 * time.Second }()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 10)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs[1:] {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 5; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := 0
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+
+	if len(psubs[0].rt.(*GossipSubRouter).fanout) == 0 {
+		t.Fatal("owner has no fanout")
+	}
+
+	// wait for TTL to expire fanout peers in owner
+	time.Sleep(time.Second * 2)
+
+	if len(psubs[0].rt.(*GossipSubRouter).fanout) > 0 {
+		t.Fatal("fanout hasn't expired")
+	}
+}
+
+func TestGossipsubGossip(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+
+		// wait a bit to have some gossip interleaved
+		time.Sleep(time.Millisecond * 100)
+	}
+
+	// and wait for some gossip flushing
+	time.Sleep(time.Second * 2)
+}
+
+func TestGossipsubGossipPiggyback(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	var xmsgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("bazcrux")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		xmsgs = append(xmsgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish("foobar", msg)
+		psubs[owner].Publish("bazcrux", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+
+		for _, sub := range xmsgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+
+		// wait a bit to have some gossip interleaved
+		time.Sleep(time.Millisecond * 100)
+	}
+
+	// and wait for some gossip flushing
+	time.Sleep(time.Second * 2)
+}
+
+func TestGossipsubGossipPropagation(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	hosts := getNetHosts(t, ctx, 20)
+	psubs := getGossipsubs(ctx, hosts)
+
+	hosts1 := hosts[:GossipSubD+1]
+	hosts2 := append(hosts[GossipSubD+1:], hosts[0])
+
+	denseConnect(t, hosts1)
+	denseConnect(t, hosts2)
+
+	var msgs1 []*Subscription
+	for _, ps := range psubs[1 : GossipSubD+1] {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs1 = append(msgs1, subch)
+	}
+
+	time.Sleep(time.Second * 1)
+
+	for i := 0; i < 10; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := 0
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs1 {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+
+	time.Sleep(time.Millisecond * 100)
+
+	var msgs2 []*Subscription
+	for _, ps := range psubs[GossipSubD+1:] {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs2 = append(msgs2, subch)
+	}
+
+	var collect [][]byte
+	for i := 0; i < 10; i++ {
+		for _, sub := range msgs2 {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			collect = append(collect, got.Data)
+		}
+	}
+
+	for i := 0; i < 10; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+		gotit := false
+		for j := 0; j < len(collect); j++ {
+			if bytes.Equal(msg, collect[j]) {
+				gotit = true
+				break
+			}
+		}
+		if !gotit {
+			t.Fatalf("Didn't get message %s", string(msg))
+		}
+	}
+}
+
+func TestGossipsubPrune(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	// disconnect some peers from the mesh to get some PRUNEs
+	for _, sub := range msgs[:5] {
+		sub.Cancel()
+	}
+
+	// wait a bit to take effect
+	time.Sleep(time.Millisecond * 100)
+
+	for i := 0; i < 10; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs[5:] {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubGraft(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	sparseConnect(t, hosts)
+
+	time.Sleep(time.Second * 1)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+
+		// wait for announce to propagate
+		time.Sleep(time.Millisecond * 100)
+	}
+
+	time.Sleep(time.Second * 1)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubRemovePeer(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 20)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	denseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	// disconnect some peers to exercise RemovePeer paths
+	for _, host := range hosts[:5] {
+		host.Close()
+	}
+
+	// wait a heartbeat
+	time.Sleep(time.Second * 1)
+
+	for i := 0; i < 10; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := 5 + rand.Intn(len(psubs)-5)
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs[5:] {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubGraftPruneRetry(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	hosts := getNetHosts(t, ctx, 10)
+	psubs := getGossipsubs(ctx, hosts)
+	denseConnect(t, hosts)
+
+	var topics []string
+	var msgs [][]*Subscription
+	for i := 0; i < 35; i++ {
+		topic := fmt.Sprintf("topic%d", i)
+		topics = append(topics, topic)
+
+		var subs []*Subscription
+		for _, ps := range psubs {
+			subch, err := ps.Subscribe(topic)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			subs = append(subs, subch)
+		}
+		msgs = append(msgs, subs)
+	}
+
+	// wait for heartbeats to build meshes
+	time.Sleep(time.Second * 5)
+
+	for i, topic := range topics {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish(topic, msg)
+
+		for _, sub := range msgs[i] {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubControlPiggyback(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	hosts := getNetHosts(t, ctx, 10)
+	psubs := getGossipsubs(ctx, hosts)
+	denseConnect(t, hosts)
+
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("flood")
+		if err != nil {
+			t.Fatal(err)
+		}
+		go func(sub *Subscription) {
+			for {
+				_, err := sub.Next(ctx)
+				if err != nil {
+					break
+				}
+			}
+		}(subch)
+	}
+
+	time.Sleep(time.Second * 1)
+
+	// create a background flood of messages that overloads the queues
+	done := make(chan struct{})
+	go func() {
+		owner := rand.Intn(len(psubs))
+		for i := 0; i < 10000; i++ {
+			msg := []byte("background flooooood")
+			psubs[owner].Publish("flood", msg)
+		}
+		done <- struct{}{}
+	}()
+
+	time.Sleep(time.Millisecond * 20)
+
+	// and subscribe to a bunch of topics in the meantime -- this should
+	// result in some dropped control messages, with subsequent piggybacking
+	// in the background flood
+	var topics []string
+	var msgs [][]*Subscription
+	for i := 0; i < 5; i++ {
+		topic := fmt.Sprintf("topic%d", i)
+		topics = append(topics, topic)
+
+		var subs []*Subscription
+		for _, ps := range psubs {
+			subch, err := ps.Subscribe(topic)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			subs = append(subs, subch)
+		}
+		msgs = append(msgs, subs)
+	}
+
+	// wait for the flood to stop
+	<-done
+
+	// and test that we have functional overlays
+	for i, topic := range topics {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish(topic, msg)
+
+		for _, sub := range msgs[i] {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestMixedGossipsub(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	hosts := getNetHosts(t, ctx, 30)
+
+	gsubs := getGossipsubs(ctx, hosts[:20])
+	fsubs := getPubsubs(ctx, hosts[20:])
+	psubs := append(gsubs, fsubs...)
+
+	var msgs []*Subscription
+	for _, ps := range psubs {
+		subch, err := ps.Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		msgs = append(msgs, subch)
+	}
+
+	sparseConnect(t, hosts)
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	for i := 0; i < 100; i++ {
+		msg := []byte(fmt.Sprintf("%d it's not a floooooood %d", i, i))
+
+		owner := rand.Intn(len(psubs))
+
+		psubs[owner].Publish("foobar", msg)
+
+		for _, sub := range msgs {
+			got, err := sub.Next(ctx)
+			if err != nil {
+				t.Fatal(sub.err)
+			}
+			if !bytes.Equal(msg, got.Data) {
+				t.Fatal("got wrong message!")
+			}
+		}
+	}
+}
+
+func TestGossipsubMultihops(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	hosts := getNetHosts(t, ctx, 6)
+
+	psubs := getGossipsubs(ctx, hosts)
+
+	connect(t, hosts[0], hosts[1])
+	connect(t, hosts[1], hosts[2])
+	connect(t, hosts[2], hosts[3])
+	connect(t, hosts[3], hosts[4])
+	connect(t, hosts[4], hosts[5])
+
+	var subs []*Subscription
+	for i := 1; i < 6; i++ {
+		ch, err := psubs[i].Subscribe("foobar")
+		if err != nil {
+			t.Fatal(err)
+		}
+		subs = append(subs, ch)
+	}
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	msg := []byte("i like cats")
+	err := psubs[0].Publish("foobar", msg)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// last node in the chain should get the message
+	select {
+	case out := <-subs[4].ch:
+		if !bytes.Equal(out.GetData(), msg) {
+			t.Fatal("got wrong data")
+		}
+	case <-time.After(time.Second * 5):
+		t.Fatal("timed out waiting for message")
+	}
+}
+
+func TestGossipsubTreeTopology(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	hosts := getNetHosts(t, ctx, 10)
+	psubs := getGossipsubs(ctx, hosts)
+
+	connect(t, hosts[0], hosts[1])
+	connect(t, hosts[1], hosts[2])
+	connect(t, hosts[1], hosts[4])
+	connect(t, hosts[2], hosts[3])
+	connect(t, hosts[0], hosts[5])
+	connect(t, hosts[5], hosts[6])
+	connect(t, hosts[5], hosts[8])
+	connect(t, hosts[6], hosts[7])
+	connect(t, hosts[8], hosts[9])
+
+	/*
+		[0] -> [1] -> [2] -> [3]
+		 |      L->[4]
+		 v
+		[5] -> [6] -> [7]
+		 |
+		 v
+		[8] -> [9]
+	*/
+
+	var chs []*Subscription
+	for _, ps := range psubs {
+		ch, err := ps.Subscribe("fizzbuzz")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		chs = append(chs, ch)
+	}
+
+	// wait for heartbeats to build mesh
+	time.Sleep(time.Second * 2)
+
+	assertPeerLists(t, hosts, psubs[0], 1, 5)
+	assertPeerLists(t, hosts, psubs[1], 0, 2, 4)
+	assertPeerLists(t, hosts, psubs[2], 1, 3)
+
+	checkMessageRouting(t, "fizzbuzz", []*PubSub{psubs[9], psubs[3]}, chs)
+}
diff --git a/mcache.go b/mcache.go
new file mode 100644
index 0000000..f501d1e
--- /dev/null
+++ b/mcache.go
@@ -0,0 +1,61 @@
+package floodsub
+
+import (
+	pb "github.com/libp2p/go-floodsub/pb"
+)
+
+func NewMessageCache(gossip, history int) *MessageCache {
+	return &MessageCache{
+		msgs:    make(map[string]*pb.Message),
+		history: make([][]CacheEntry, history),
+		gossip:  gossip,
+	}
+}
+
+type MessageCache struct {
+	msgs    map[string]*pb.Message
+	history [][]CacheEntry
+	gossip  int
+}
+
+type CacheEntry struct {
+	mid    string
+	topics []string
+}
+
+func (mc *MessageCache) Put(msg *pb.Message) {
+	mid := msgID(msg)
+	mc.msgs[mid] = msg
+	mc.history[0] = append(mc.history[0], CacheEntry{mid: mid, topics: msg.GetTopicIDs()})
+}
+
+func (mc *MessageCache) Get(mid string) (*pb.Message, bool) {
+	m, ok := mc.msgs[mid]
+	return m, ok
+}
+
+func (mc *MessageCache) GetGossipIDs(topic string) []string {
+	var mids []string
+	for _, entries := range mc.history[:mc.gossip] {
+		for _, entry := range entries {
+			for _, t := range entry.topics {
+				if t == topic {
+					mids = append(mids, entry.mid)
+					break
+				}
+			}
+		}
+	}
+	return mids
+}
+
+func (mc *MessageCache) Shift() {
+	last := mc.history[len(mc.history)-1]
+	for _, entry := range last {
+		delete(mc.msgs, entry.mid)
+	}
+	for i := len(mc.history) - 2; i >= 0; i-- {
+		mc.history[i+1] = mc.history[i]
+	}
+	mc.history[0] = nil
+}
diff --git a/mcache_test.go b/mcache_test.go
new file mode 100644
index 0000000..6bc526c
--- /dev/null
+++ b/mcache_test.go
@@ -0,0 +1,165 @@
+package floodsub
+
+import (
+	"encoding/binary"
+	"fmt"
+	"testing"
+
+	pb "github.com/libp2p/go-floodsub/pb"
+)
+
+func TestMessageCache(t *testing.T) {
+	mcache := NewMessageCache(3, 5)
+
+	msgs := make([]*pb.Message, 60)
+	for i := range msgs {
+		msgs[i] = makeTestMessage(i)
+	}
+
+	for i := 0; i < 10; i++ {
+		mcache.Put(msgs[i])
+	}
+
+	for i := 0; i < 10; i++ {
+		mid := msgID(msgs[i])
+		m, ok := mcache.Get(mid)
+		if !ok {
+			t.Fatalf("Message %d not in cache", i)
+		}
+
+		if m != msgs[i] {
+			t.Fatalf("Message %d does not match cache", i)
+		}
+	}
+
+	gids := mcache.GetGossipIDs("test")
+	if len(gids) != 10 {
+		t.Fatalf("Expected 10 gossip IDs; got %d", len(gids))
+	}
+
+	for i := 0; i < 10; i++ {
+		mid := msgID(msgs[i])
+		if mid != gids[i] {
+			t.Fatalf("GossipID mismatch for message %d", i)
+		}
+	}
+
+	mcache.Shift()
+	for i := 10; i < 20; i++ {
+		mcache.Put(msgs[i])
+	}
+
+	for i := 0; i < 20; i++ {
+		mid := msgID(msgs[i])
+		m, ok := mcache.Get(mid)
+		if !ok {
+			t.Fatalf("Message %d not in cache", i)
+		}
+
+		if m != msgs[i] {
+			t.Fatalf("Message %d does not match cache", i)
+		}
+	}
+
+	gids = mcache.GetGossipIDs("test")
+	if len(gids) != 20 {
+		t.Fatalf("Expected 20 gossip IDs; got %d", len(gids))
+	}
+
+	for i := 0; i < 10; i++ {
+		mid := msgID(msgs[i])
+		if mid != gids[10+i] {
+			t.Fatalf("GossipID mismatch for message %d", i)
+		}
+	}
+
+	for i := 10; i < 20; i++ {
+		mid := msgID(msgs[i])
+		if mid != gids[i-10] {
+			t.Fatalf("GossipID mismatch for message %d", i)
+		}
+	}
+
+	mcache.Shift()
+	for i := 20; i < 30; i++ {
+		mcache.Put(msgs[i])
+	}
+
+	mcache.Shift()
+	for i := 30; i < 40; i++ {
+		mcache.Put(msgs[i])
+	}
+
+	mcache.Shift()
+	for i := 40; i < 50; i++ {
+		mcache.Put(msgs[i])
+	}
+
+	mcache.Shift()
+	for i := 50; i < 60; i++ {
+		mcache.Put(msgs[i])
+	}
+
+	if len(mcache.msgs) != 50 {
+		t.Fatalf("Expected 50 messages in the cache; got %d", len(mcache.msgs))
+	}
+
+	for i := 0; i < 10; i++ {
+		mid := msgID(msgs[i])
+		_, ok := mcache.Get(mid)
+		if ok {
+			t.Fatalf("Message %d still in cache", i)
+		}
+	}
+
+	for i := 10; i < 60; i++ {
+		mid := msgID(msgs[i])
+		m, ok := mcache.Get(mid)
+		if !ok {
+			t.Fatalf("Message %d not in cache", i)
+		}
+
+		if m != msgs[i] {
+			t.Fatalf("Message %d does not match cache", i)
+		}
+	}
+
+	gids = mcache.GetGossipIDs("test")
+	if len(gids) != 30 {
+		t.Fatalf("Expected 30 gossip IDs; got %d", len(gids))
+	}
+
+	for i := 0; i < 10; i++ {
+		mid := msgID(msgs[50+i])
+		if mid != gids[i] {
+			t.Fatalf("GossipID mismatch for message %d", i)
+		}
+	}
+
+	for i := 10; i < 20; i++ {
+		mid := msgID(msgs[30+i])
+		if mid != gids[i] {
+			t.Fatalf("GossipID mismatch for message %d", i)
+		}
+	}
+
+	for i := 20; i < 30; i++ {
+		mid := msgID(msgs[10+i])
+		if mid != gids[i] {
+			t.Fatalf("GossipID mismatch for message %d", i)
+		}
+	}
+
+}
+
+func makeTestMessage(n int) *pb.Message {
+	seqno := make([]byte, 8)
+	binary.BigEndian.PutUint64(seqno, uint64(n))
+	data := []byte(fmt.Sprintf("%d", n))
+	return &pb.Message{
+		Data:     data,
+		TopicIDs: []string{"test"},
+		From:     []byte("test"),
+		Seqno:    seqno,
+	}
+}
diff --git a/pb/rpc.pb.go b/pb/rpc.pb.go
index a5933c0..f970bbc 100644
--- a/pb/rpc.pb.go
+++ b/pb/rpc.pb.go
@@ -11,6 +11,11 @@ It is generated from these files:
 It has these top-level messages:
 	RPC
 	Message
+	ControlMessage
+	ControlIHave
+	ControlIWant
+	ControlGraft
+	ControlPrune
 	TopicDescriptor
 */
 package floodsub_pb
@@ -97,9 +102,10 @@ func (x *TopicDescriptor_EncOpts_EncMode) UnmarshalJSON(data []byte) error {
 }
 
 type RPC struct {
-	Subscriptions    []*RPC_SubOpts `protobuf:"bytes,1,rep,name=subscriptions" json:"subscriptions,omitempty"`
-	Publish          []*Message     `protobuf:"bytes,2,rep,name=publish" json:"publish,omitempty"`
-	XXX_unrecognized []byte         `json:"-"`
+	Subscriptions    []*RPC_SubOpts  `protobuf:"bytes,1,rep,name=subscriptions" json:"subscriptions,omitempty"`
+	Publish          []*Message      `protobuf:"bytes,2,rep,name=publish" json:"publish,omitempty"`
+	Control          *ControlMessage `protobuf:"bytes,3,opt,name=control" json:"control,omitempty"`
+	XXX_unrecognized []byte          `json:"-"`
 }
 
 func (m *RPC) Reset()         { *m = RPC{} }
@@ -120,6 +126,13 @@ func (m *RPC) GetPublish() []*Message {
 	return nil
 }
 
+func (m *RPC) GetControl() *ControlMessage {
+	if m != nil {
+		return m.Control
+	}
+	return nil
+}
+
 type RPC_SubOpts struct {
 	Subscribe        *bool   `protobuf:"varint,1,opt,name=subscribe" json:"subscribe,omitempty"`
 	Topicid          *string `protobuf:"bytes,2,opt,name=topicid" json:"topicid,omitempty"`
@@ -184,6 +197,118 @@ func (m *Message) GetTopicIDs() []string {
 	return nil
 }
 
+type ControlMessage struct {
+	Ihave            []*ControlIHave `protobuf:"bytes,1,rep,name=ihave" json:"ihave,omitempty"`
+	Iwant            []*ControlIWant `protobuf:"bytes,2,rep,name=iwant" json:"iwant,omitempty"`
+	Graft            []*ControlGraft `protobuf:"bytes,3,rep,name=graft" json:"graft,omitempty"`
+	Prune            []*ControlPrune `protobuf:"bytes,4,rep,name=prune" json:"prune,omitempty"`
+	XXX_unrecognized []byte          `json:"-"`
+}
+
+func (m *ControlMessage) Reset()         { *m = ControlMessage{} }
+func (m *ControlMessage) String() string { return proto.CompactTextString(m) }
+func (*ControlMessage) ProtoMessage()    {}
+
+func (m *ControlMessage) GetIhave() []*ControlIHave {
+	if m != nil {
+		return m.Ihave
+	}
+	return nil
+}
+
+func (m *ControlMessage) GetIwant() []*ControlIWant {
+	if m != nil {
+		return m.Iwant
+	}
+	return nil
+}
+
+func (m *ControlMessage) GetGraft() []*ControlGraft {
+	if m != nil {
+		return m.Graft
+	}
+	return nil
+}
+
+func (m *ControlMessage) GetPrune() []*ControlPrune {
+	if m != nil {
+		return m.Prune
+	}
+	return nil
+}
+
+type ControlIHave struct {
+	TopicID          *string  `protobuf:"bytes,1,opt,name=topicID" json:"topicID,omitempty"`
+	MessageIDs       []string `protobuf:"bytes,2,rep,name=messageIDs" json:"messageIDs,omitempty"`
+	XXX_unrecognized []byte   `json:"-"`
+}
+
+func (m *ControlIHave) Reset()         { *m = ControlIHave{} }
+func (m *ControlIHave) String() string { return proto.CompactTextString(m) }
+func (*ControlIHave) ProtoMessage()    {}
+
+func (m *ControlIHave) GetTopicID() string {
+	if m != nil && m.TopicID != nil {
+		return *m.TopicID
+	}
+	return ""
+}
+
+func (m *ControlIHave) GetMessageIDs() []string {
+	if m != nil {
+		return m.MessageIDs
+	}
+	return nil
+}
+
+type ControlIWant struct {
+	MessageIDs       []string `protobuf:"bytes,1,rep,name=messageIDs" json:"messageIDs,omitempty"`
+	XXX_unrecognized []byte   `json:"-"`
+}
+
+func (m *ControlIWant) Reset()         { *m = ControlIWant{} }
+func (m *ControlIWant) String() string { return proto.CompactTextString(m) }
+func (*ControlIWant) ProtoMessage()    {}
+
+func (m *ControlIWant) GetMessageIDs() []string {
+	if m != nil {
+		return m.MessageIDs
+	}
+	return nil
+}
+
+type ControlGraft struct {
+	TopicID          *string `protobuf:"bytes,1,opt,name=topicID" json:"topicID,omitempty"`
+	XXX_unrecognized []byte  `json:"-"`
+}
+
+func (m *ControlGraft) Reset()         { *m = ControlGraft{} }
+func (m *ControlGraft) String() string { return proto.CompactTextString(m) }
+func (*ControlGraft) ProtoMessage()    {}
+
+func (m *ControlGraft) GetTopicID() string {
+	if m != nil && m.TopicID != nil {
+		return *m.TopicID
+	}
+	return ""
+}
+
+type ControlPrune struct {
+	TopicID          *string `protobuf:"bytes,1,opt,name=topicID" json:"topicID,omitempty"`
+	XXX_unrecognized []byte  `json:"-"`
+}
+
+func (m *ControlPrune) Reset()         { *m = ControlPrune{} }
+func (m *ControlPrune) String() string { return proto.CompactTextString(m) }
+func (*ControlPrune) ProtoMessage()    {}
+
+func (m *ControlPrune) GetTopicID() string {
+	if m != nil && m.TopicID != nil {
+		return *m.TopicID
+	}
+	return ""
+}
+
 // topicID = hash(topicDescriptor); (not the topic.name)
 type TopicDescriptor struct {
 	Name             *string                   `protobuf:"bytes,1,opt,name=name" json:"name,omitempty"`
@@ -269,6 +394,11 @@ func init() {
 	proto.RegisterType((*RPC)(nil), "floodsub.pb.RPC")
 	proto.RegisterType((*RPC_SubOpts)(nil), "floodsub.pb.RPC.SubOpts")
 	proto.RegisterType((*Message)(nil), "floodsub.pb.Message")
+	proto.RegisterType((*ControlMessage)(nil), "floodsub.pb.ControlMessage")
+	proto.RegisterType((*ControlIHave)(nil), "floodsub.pb.ControlIHave")
+	proto.RegisterType((*ControlIWant)(nil), "floodsub.pb.ControlIWant")
+	proto.RegisterType((*ControlGraft)(nil), "floodsub.pb.ControlGraft")
+	proto.RegisterType((*ControlPrune)(nil), "floodsub.pb.ControlPrune")
 	proto.RegisterType((*TopicDescriptor)(nil), "floodsub.pb.TopicDescriptor")
 	proto.RegisterType((*TopicDescriptor_AuthOpts)(nil), "floodsub.pb.TopicDescriptor.AuthOpts")
 	proto.RegisterType((*TopicDescriptor_EncOpts)(nil), "floodsub.pb.TopicDescriptor.EncOpts")
diff --git a/pb/rpc.proto b/pb/rpc.proto
index f43d3c1..a7fe600 100644
--- a/pb/rpc.proto
+++ b/pb/rpc.proto
@@ -8,6 +8,8 @@ message RPC {
 		optional bool subscribe = 1; // subscribe or unsubcribe
 		optional string topicid = 2;
 	}
+
+    optional ControlMessage control = 3;
 }
 
 message Message {
@@ -17,6 +19,30 @@ message Message {
 	repeated string topicIDs = 4;
 }
 
+message ControlMessage {
+    repeated ControlIHave ihave = 1;
+    repeated ControlIWant iwant = 2;
+    repeated ControlGraft graft = 3;
+    repeated ControlPrune prune = 4;
+}
+
+message ControlIHave {
+    optional string topicID = 1;
+    repeated string messageIDs = 2;
+}
+
+message ControlIWant {
+    repeated string messageIDs = 1;
+}
+
+message ControlGraft {
+    optional string topicID = 1;
+}
+
+message ControlPrune {
+    optional string topicID = 1;
+}
+
 // topicID = hash(topicDescriptor); (not the topic.name)
 message TopicDescriptor {
 	optional string name = 1;
diff --git a/pubsub.go b/pubsub.go
index 5d92af9..4d5415a 100644
--- a/pubsub.go
+++ b/pubsub.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/binary"
 	"fmt"
+	"math/rand"
 	"sync/atomic"
 	"time"
 
@@ -82,6 +83,9 @@ type PubSub struct {
 	// validateThrottle limits the number of active validation goroutines
 	validateThrottle chan struct{}
 
+	// eval thunk in event loop
+	eval chan func()
+
 	peers        map[peer.ID]chan *RPC
 	seenMessages *timecache.TimeCache
 
@@ -90,12 +94,26 @@ type PubSub struct {
 
 // PubSubRouter is the message router component of PubSub
 type PubSubRouter interface {
+	// Protocols returns the list of protocols supported by the router.
 	Protocols() []protocol.ID
+	// Attach is invoked by the PubSub constructor to attach the router to a
+	// freshly initialized PubSub instance.
 	Attach(*PubSub)
+	// AddPeer notifies the router that a new peer has been connected.
 	AddPeer(peer.ID, protocol.ID)
+	// RemovePeer notifies the router that a peer has been disconnected.
 	RemovePeer(peer.ID)
+	// HandleRPC is invoked to process control messages in the RPC envelope.
+	// It is invoked after subscriptions and payload messages have been processed.
 	HandleRPC(*RPC)
+	// Publish is invoked to forward a new message that has been validated.
 	Publish(peer.ID, *pb.Message)
+	// Join notifies the router that we want to receive and forward messages in a topic.
+	// It is invoked after the subscription announcement.
+	Join(topic string)
+	// Leave notifies the router that we are no longer interested in a topic.
+	// It is invoked after the unsubscription announcement.
+	Leave(topic string)
 }
 
 type Message struct {
@@ -115,7 +133,7 @@ type RPC struct {
 
 type Option func(*PubSub) error
 
-// NewFloodSub returns a new PubSub management object
+// NewPubSub returns a new PubSub management object
 func NewPubSub(ctx context.Context, h host.Host, rt PubSubRouter, opts ...Option) (*PubSub, error) {
 	ps := &PubSub{
 		host:             h,
@@ -133,11 +151,12 @@ func NewPubSub(ctx context.Context, h host.Host, rt PubSubRouter, opts ...Option
 		addVal:           make(chan *addValReq),
 		rmVal:            make(chan *rmValReq),
 		validateThrottle: make(chan struct{}, defaultValidateThrottle),
+		eval:             make(chan func()),
 		myTopics:         make(map[string]map[*Subscription]struct{}),
 		topics:           make(map[string]map[peer.ID]struct{}),
 		peers:            make(map[peer.ID]chan *RPC),
 		topicVals:        make(map[string]*topicVal),
-		seenMessages:     timecache.NewTimeCache(time.Second * 30),
+		seenMessages:     timecache.NewTimeCache(time.Second * 120),
 		counter:          uint64(time.Now().UnixNano()),
 	}
 
@@ -243,7 +262,7 @@ func (p *PubSub) processLoop(ctx context.Context) {
 			p.pushMsg(vals, p.host.ID(), msg)
 
 		case req := <-p.sendMsg:
-			p.maybePublishMessage(req.from, req.msg.Message)
+			p.publishMessage(req.from, req.msg.Message)
 
 		case req := <-p.addVal:
 			p.addValidator(req)
@@ -251,6 +270,9 @@ func (p *PubSub) processLoop(ctx context.Context) {
 		case req := <-p.rmVal:
 			p.rmValidator(req)
 
+		case thunk := <-p.eval:
+			thunk()
+
 		case <-ctx.Done():
 			log.Info("pubsub processloop shutting down")
 			return
@@ -276,6 +298,7 @@ func (p *PubSub) handleRemoveSubscription(sub *Subscription) {
 	if len(subs) == 0 {
 		delete(p.myTopics, sub.topic)
 		p.announce(sub.topic, false)
+		p.rt.Leave(sub.topic)
 	}
 }
 
@@ -290,6 +313,7 @@ func (p *PubSub) handleAddSubscription(req *addSubReq) {
 	// announce we want this topic
 	if len(subs) == 0 {
 		p.announce(sub.topic, true)
+		p.rt.Join(sub.topic)
 	}
 
 	// make new if not there
@@ -319,11 +343,28 @@ func (p *PubSub) announce(topic string, sub bool) {
 		select {
 		case peer <- out:
 		default:
-			log.Infof("dropping announce message to peer %s: queue full", pid)
+			log.Infof("Can't send announce message to peer %s: queue full; scheduling retry", pid)
+			go p.announceRetry(topic, sub)
 		}
 	}
 }
 
+func (p *PubSub) announceRetry(topic string, sub bool) {
+	time.Sleep(time.Duration(1+rand.Intn(1000)) * time.Millisecond)
+
+	retry := func() {
+		_, ok := p.myTopics[topic]
+		if (ok && sub) || (!ok && !sub) {
+			p.announce(topic, sub)
+		}
+	}
+
+	select {
+	case p.eval <- retry:
+	case <-p.ctx.Done():
+	}
+}
+
 // notifySubs sends a given message to all corresponding subscribers.
 // Only called from processLoop.
 func (p *PubSub) notifySubs(msg *pb.Message) {
@@ -405,6 +446,12 @@ func msgID(pmsg *pb.Message) string {
 
 // pushMsg pushes a message performing validation as necessary
 func (p *PubSub) pushMsg(vals []*topicVal, src peer.ID, msg *Message) {
+	id := msgID(msg.Message)
+	if p.seenMessage(id) {
+		return
+	}
+	p.markSeen(id)
+
 	if len(vals) > 0 {
 		// validation is asynchronous and globally throttled with the throttleValidate semaphore.
 		// the purpose of the global throttle is to bound the goncurrency possible from incoming
@@ -422,7 +469,7 @@ func (p *PubSub) pushMsg(vals []*topicVal, src peer.ID, msg *Message) {
 		return
 	}
 
-	p.maybePublishMessage(src, msg.Message)
+	p.publishMessage(src, msg.Message)
 }
 
 // validate performs validation and only sends the message if all validators succeed
@@ -472,13 +519,7 @@ loop:
 	}
 }
 
-func (p *PubSub) maybePublishMessage(from peer.ID, pmsg *pb.Message) {
-	id := msgID(pmsg)
-	if p.seenMessage(id) {
-		return
-	}
-
-	p.markSeen(id)
+func (p *PubSub) publishMessage(from peer.ID, pmsg *pb.Message) {
 	p.notifySubs(pmsg)
 	p.rt.Publish(from, pmsg)
 }
@@ -556,10 +597,7 @@ func (p *PubSub) GetTopics() []string {
 
 // Publish publishes data under the given topic
 func (p *PubSub) Publish(topic string, data []byte) error {
-	seqno := make([]byte, 8)
-	counter := atomic.AddUint64(&p.counter, 1)
-	binary.BigEndian.PutUint64(seqno, counter)
-
+	seqno := p.nextSeqno()
 	p.publish <- &Message{
 		&pb.Message{
 			Data:     data,
@@ -571,12 +609,20 @@ func (p *PubSub) Publish(topic string, data []byte) error {
 	return nil
 }
 
+func (p *PubSub) nextSeqno() []byte {
+	seqno := make([]byte, 8)
+	counter := atomic.AddUint64(&p.counter, 1)
+	binary.BigEndian.PutUint64(seqno, counter)
+	return seqno
+}
+
 type listPeerReq struct {
 	resp  chan []peer.ID
 	topic string
 }
 
-// sendReq is a request to call maybePublishMessage. It is issued after the subscription verification is done.
+// sendReq is a request to call publishMessage.
+// It is issued after message validation is done.
 type sendReq struct {
 	from peer.ID
 	msg  *Message