diff --git a/gossipsub.go b/gossipsub.go
index e7d469a..d34bfff 100644
--- a/gossipsub.go
+++ b/gossipsub.go
@@ -68,27 +68,19 @@ func (gs *GossipSubRouter) HandleRPC(rpc *RPC) {
 	}
 
 	iwant := gs.handleIHave(ctl)
-	msgs := gs.handleIWant(ctl)
+	ihave := gs.handleIWant(ctl)
 	prune := gs.handleGraft(rpc.from, ctl)
 	gs.handlePrune(rpc.from, ctl)
 
-	if len(iwant) == 0 && len(msgs) == 0 && len(prune) == 0 {
+	if len(iwant) == 0 && len(ihave) == 0 && len(prune) == 0 {
 		return
 	}
 
-	// TODO piggyback gossip IHAVE
-	out := rpcWithControl(msgs, nil, iwant, nil, prune)
-
-	mch, ok := gs.p.peers[rpc.from]
-	if !ok {
-		return
-	}
-
-	select {
-	case mch <- out:
-	default:
-		// TODO PRUNE messages should be reliable; schedule for piggybacking or retry
-		log.Infof("dropping message to peer %s: queue full", rpc.from)
+	out := rpcWithControl(ihave, nil, iwant, nil, prune)
+	if len(prune) == 0 {
+		gs.sendMessage(rpc.from, out)
+	} else {
+		gs.sendControl(rpc.from, out)
 	}
 }
 
@@ -207,12 +199,7 @@ func (gs *GossipSubRouter) Publish(from peer.ID, msg *pb.Message) {
 				peers := gs.getPeers(topic, func(peer.ID) bool { return true })
 
 				if len(peers) > 0 {
-					gmap = make(map[peer.ID]struct{})
-
-					for _, p := range peers[:GossipSubD] {
-						gmap[p] = struct{}{}
-					}
-
+					gmap = peerListToMap(peers[:GossipSubD])
 					gs.fanout[topic] = gmap
 				}
 			}
@@ -229,17 +216,78 @@ func (gs *GossipSubRouter) Publish(from peer.ID, msg *pb.Message) {
 			continue
 		}
 
-		mch, ok := gs.p.peers[pid]
-		if !ok {
-			continue
-		}
+		gs.sendMessage(pid, out)
+	}
+}
 
-		select {
-		case mch <- out:
-		default:
-			log.Infof("dropping message to peer %s: queue full", pid)
-			// Drop it. The peer is too slow.
-		}
+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)
+	} else {
+		peers := gs.getPeers(topic, func(peer.ID) bool { return true })
+		gmap = peerListToMap(peers[:GossipSubD])
+		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
+	}
+
+	for p := range gmap {
+		gs.sendPrune(p, topic)
+	}
+	delete(gs.mesh, 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.sendControl(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.sendControl(p, out)
+}
+
+func (gs *GossipSubRouter) sendControl(p peer.ID, out *RPC) {
+	gs.sendRPC(p, out, true)
+}
+
+func (gs *GossipSubRouter) sendMessage(p peer.ID, out *RPC) {
+	gs.sendRPC(p, out, false)
+}
+
+func (gs *GossipSubRouter) sendRPC(p peer.ID, out *RPC, ctl bool) {
+	// TODO control messages and gossip piggyback
+	// - control messages (GRAFT/PRUNE) must be reliable and should
+	//   be scheduled for piggyback or retry if the queue is full
+	// - gossip should be piggybacked on messages oppurtinistcally
+
+	mch, ok := gs.p.peers[p]
+	if !ok {
+		return
+	}
+
+	select {
+	case mch <- out:
+	default:
+		log.Infof("dropping message to peer %s: queue full", p)
 	}
 }
 
@@ -261,14 +309,6 @@ func (gs *GossipSubRouter) getPeers(topic string, filter func(peer.ID) bool) []p
 	return peers
 }
 
-func (gs *GossipSubRouter) Join(topic string) {
-	// TODO
-}
-
-func (gs *GossipSubRouter) Leave(topic string) {
-	// TODO
-}
-
 func (gs *GossipSubRouter) heartbeatTimer() {
 	ticker := time.NewTicker(1 * time.Second)
 	defer ticker.Stop()
@@ -291,6 +331,14 @@ func (gs *GossipSubRouter) heartbeat() {
 	// TODO
 }
 
+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 shufflePeers(peers []peer.ID) {
 	// TODO
 }