diff --git a/score.go b/score.go
index 55c9f6f..bfddde1 100644
--- a/score.go
+++ b/score.go
@@ -1,6 +1,7 @@
 package pubsub
 
 import (
+	"context"
 	"sync"
 	"time"
 
@@ -180,13 +181,20 @@ const (
 )
 
 func newPeerScore(params *PeerScoreParams) *peerScore {
-	// TODO
-	return nil
+	return &peerScore{
+		params:     params,
+		peerStats:  make(map[peer.ID]*peerStats),
+		peerIPs:    make(map[string]map[peer.ID]struct{}),
+		deliveries: &messageDeliveries{records: make(map[string]*deliveryRecord)},
+		msgID:      DefaultMsgIdFn,
+	}
 }
 
 // router interface
 func (ps *peerScore) Start(gs *GossipSubRouter) {
-	// TODO
+	ps.msgID = gs.p.msgID
+	ps.host = gs.p.host
+	go ps.background(gs.p.ctx)
 }
 
 func (ps *peerScore) Score(p peer.ID) float64 {
@@ -268,6 +276,33 @@ func (ps *peerScore) Score(p peer.ID) float64 {
 }
 
 // periodic maintenance
+func (ps *peerScore) background(ctx context.Context) {
+	refreshScores := time.NewTicker(ps.params.DecayInterval)
+	defer refreshScores.Stop()
+
+	refreshIPs := time.NewTicker(time.Minute)
+	defer refreshIPs.Stop()
+
+	gcDeliveryRecords := time.NewTicker(time.Minute)
+	defer gcDeliveryRecords.Stop()
+
+	for {
+		select {
+		case <-refreshScores.C:
+			ps.refreshScores()
+
+		case <-refreshIPs.C:
+			ps.refreshIPs()
+
+		case <-gcDeliveryRecords.C:
+			ps.gcDeliveryRecords()
+
+		case <-ctx.Done():
+			return
+		}
+	}
+}
+
 func (ps *peerScore) refreshScores() {
 	ps.Lock()
 	defer ps.Unlock()
@@ -325,7 +360,10 @@ func (ps *peerScore) refreshScores() {
 	}
 }
 
-func (ps *peerScore) resfreshIPs() {
+func (ps *peerScore) refreshIPs() {
+	ps.Lock()
+	defer ps.Unlock()
+
 	// peer IPs may change, so we periodically refresh them
 	for p, pstats := range ps.peerStats {
 		if pstats.connected {
@@ -336,6 +374,13 @@ func (ps *peerScore) resfreshIPs() {
 	}
 }
 
+func (ps *peerScore) gcDeliveryRecords() {
+	ps.Lock()
+	defer ps.Unlock()
+
+	ps.deliveries.gc()
+}
+
 // tracer interface
 func (ps *peerScore) AddPeer(p peer.ID, proto protocol.ID) {
 	ps.Lock()