diff --git a/internal/ackhandler/sent_packet_handler.go b/internal/ackhandler/sent_packet_handler.go
index b22cafd97..2332dcf73 100644
--- a/internal/ackhandler/sent_packet_handler.go
+++ b/internal/ackhandler/sent_packet_handler.go
@@ -103,6 +103,7 @@ func newSentPacketHandler(
 		congestion.DefaultClock{},
 		rttStats,
 		true, // use Reno
+		tracer,
 	)
 
 	return &sentPacketHandler{
diff --git a/internal/congestion/cubic_sender.go b/internal/congestion/cubic_sender.go
index 2279c3312..07f6cbd34 100644
--- a/internal/congestion/cubic_sender.go
+++ b/internal/congestion/cubic_sender.go
@@ -5,6 +5,7 @@ import (
 
 	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/utils"
+	"github.com/lucas-clemente/quic-go/logging"
 )
 
 const (
@@ -57,17 +58,20 @@ type cubicSender struct {
 
 	initialCongestionWindow    protocol.ByteCount
 	initialMaxCongestionWindow protocol.ByteCount
+
+	lastState logging.CongestionState
+	tracer    logging.ConnectionTracer
 }
 
 var _ SendAlgorithm = &cubicSender{}
 var _ SendAlgorithmWithDebugInfos = &cubicSender{}
 
 // NewCubicSender makes a new cubic sender
-func NewCubicSender(clock Clock, rttStats *utils.RTTStats, reno bool) *cubicSender {
-	return newCubicSender(clock, rttStats, reno, initialCongestionWindow, maxCongestionWindow)
+func NewCubicSender(clock Clock, rttStats *utils.RTTStats, reno bool, tracer logging.ConnectionTracer) *cubicSender {
+	return newCubicSender(clock, rttStats, reno, initialCongestionWindow, maxCongestionWindow, tracer)
 }
 
-func newCubicSender(clock Clock, rttStats *utils.RTTStats, reno bool, initialCongestionWindow, initialMaxCongestionWindow protocol.ByteCount) *cubicSender {
+func newCubicSender(clock Clock, rttStats *utils.RTTStats, reno bool, initialCongestionWindow, initialMaxCongestionWindow protocol.ByteCount, tracer logging.ConnectionTracer) *cubicSender {
 	c := &cubicSender{
 		rttStats:                   rttStats,
 		largestSentPacketNumber:    protocol.InvalidPacketNumber,
@@ -82,8 +86,13 @@ func newCubicSender(clock Clock, rttStats *utils.RTTStats, reno bool, initialCon
 		cubic:                      NewCubic(clock),
 		clock:                      clock,
 		reno:                       reno,
+		tracer:                     tracer,
 	}
 	c.pacer = newPacer(c.BandwidthEstimate)
+	if c.tracer != nil {
+		c.lastState = logging.CongestionStateSlowStart
+		c.tracer.UpdatedCongestionState(logging.CongestionStateSlowStart)
+	}
 	return c
 }
 
@@ -131,6 +140,7 @@ func (c *cubicSender) MaybeExitSlowStart() {
 	if c.InSlowStart() && c.hybridSlowStart.ShouldExitSlowStart(c.rttStats.LatestRTT(), c.rttStats.MinRTT(), c.GetCongestionWindow()/maxDatagramSize) {
 		// exit slow start
 		c.slowStartThreshold = c.congestionWindow
+		c.maybeTraceStateChange(logging.CongestionStateCongestionAvoidance)
 	}
 }
 
@@ -161,6 +171,7 @@ func (c *cubicSender) OnPacketLost(
 		return
 	}
 	c.lastCutbackExitedSlowstart = c.InSlowStart()
+	c.maybeTraceStateChange(logging.CongestionStateRecovery)
 
 	if c.reno {
 		c.congestionWindow = protocol.ByteCount(float64(c.congestionWindow) * renoBeta)
@@ -189,6 +200,7 @@ func (c *cubicSender) maybeIncreaseCwnd(
 	// the current window.
 	if !c.isCwndLimited(priorInFlight) {
 		c.cubic.OnApplicationLimited()
+		c.maybeTraceStateChange(logging.CongestionStateApplicationLimited)
 		return
 	}
 	if c.congestionWindow >= c.maxCongestionWindow {
@@ -197,9 +209,11 @@ func (c *cubicSender) maybeIncreaseCwnd(
 	if c.InSlowStart() {
 		// TCP slow start, exponential growth, increase by one for each ACK.
 		c.congestionWindow += maxDatagramSize
+		c.maybeTraceStateChange(logging.CongestionStateSlowStart)
 		return
 	}
 	// Congestion avoidance
+	c.maybeTraceStateChange(logging.CongestionStateCongestionAvoidance)
 	if c.reno {
 		// Classic Reno congestion avoidance.
 		c.numAckedPackets++
@@ -257,3 +271,10 @@ func (c *cubicSender) OnConnectionMigration() {
 	c.slowStartThreshold = c.initialMaxCongestionWindow
 	c.maxCongestionWindow = c.initialMaxCongestionWindow
 }
+
+func (c *cubicSender) maybeTraceStateChange(new logging.CongestionState) {
+	if c.tracer == nil || new == c.lastState {
+		return
+	}
+	c.tracer.UpdatedCongestionState(new)
+}
diff --git a/internal/congestion/cubic_sender_test.go b/internal/congestion/cubic_sender_test.go
index 6490a3d87..b341ee7a3 100644
--- a/internal/congestion/cubic_sender_test.go
+++ b/internal/congestion/cubic_sender_test.go
@@ -40,7 +40,7 @@ var _ = Describe("Cubic Sender", func() {
 		ackedPacketNumber = 0
 		clock = mockClock{}
 		rttStats = utils.NewRTTStats()
-		sender = newCubicSender(&clock, rttStats, true /*reno*/, initialCongestionWindowPackets*maxDatagramSize, MaxCongestionWindow)
+		sender = newCubicSender(&clock, rttStats, true /*reno*/, initialCongestionWindowPackets*maxDatagramSize, MaxCongestionWindow, nil)
 	})
 
 	SendAvailableSendWindowLen := func(packetLength protocol.ByteCount) int {
@@ -308,7 +308,7 @@ var _ = Describe("Cubic Sender", func() {
 	It("tcp cubic reset epoch on quiescence", func() {
 		const maxCongestionWindow = 50
 		const maxCongestionWindowBytes = maxCongestionWindow * maxDatagramSize
-		sender = newCubicSender(&clock, rttStats, false, initialCongestionWindowPackets*maxDatagramSize, maxCongestionWindowBytes)
+		sender = newCubicSender(&clock, rttStats, false, initialCongestionWindowPackets*maxDatagramSize, maxCongestionWindowBytes, nil)
 
 		numSent := SendAvailableSendWindow()
 
@@ -448,7 +448,7 @@ var _ = Describe("Cubic Sender", func() {
 	})
 
 	It("default max cwnd", func() {
-		sender = newCubicSender(&clock, rttStats, true /*reno*/, initialCongestionWindowPackets*maxDatagramSize, maxCongestionWindow)
+		sender = newCubicSender(&clock, rttStats, true /*reno*/, initialCongestionWindowPackets*maxDatagramSize, maxCongestionWindow, nil)
 
 		defaultMaxCongestionWindowPackets := maxCongestionWindow / maxDatagramSize
 		for i := 1; i < int(defaultMaxCongestionWindowPackets); i++ {
@@ -460,7 +460,7 @@ var _ = Describe("Cubic Sender", func() {
 
 	It("limit cwnd increase in congestion avoidance", func() {
 		// Enable Cubic.
-		sender = newCubicSender(&clock, rttStats, false, initialCongestionWindowPackets*maxDatagramSize, MaxCongestionWindow)
+		sender = newCubicSender(&clock, rttStats, false, initialCongestionWindowPackets*maxDatagramSize, MaxCongestionWindow, nil)
 		numSent := SendAvailableSendWindow()
 
 		// Make sure we fall out of slow start.
diff --git a/internal/mocks/connection_tracer.go b/internal/mocks/connection_tracer.go
index 5581db743..aac749ba6 100644
--- a/internal/mocks/connection_tracer.go
+++ b/internal/mocks/connection_tracer.go
@@ -5,16 +5,15 @@
 package mocks
 
 import (
-	"net"
-	"reflect"
-	"time"
+	net "net"
+	reflect "reflect"
+	time "time"
 
-	"github.com/lucas-clemente/quic-go/internal/utils"
-
-	"github.com/golang/mock/gomock"
-	"github.com/lucas-clemente/quic-go/internal/protocol"
-	"github.com/lucas-clemente/quic-go/internal/wire"
-	"github.com/lucas-clemente/quic-go/logging"
+	gomock "github.com/golang/mock/gomock"
+	protocol "github.com/lucas-clemente/quic-go/internal/protocol"
+	utils "github.com/lucas-clemente/quic-go/internal/utils"
+	wire "github.com/lucas-clemente/quic-go/internal/wire"
+	logging "github.com/lucas-clemente/quic-go/logging"
 )
 
 // MockConnectionTracer is a mock of ConnectionTracer interface
@@ -232,6 +231,18 @@ func (mr *MockConnectionTracerMockRecorder) StartedConnection(arg0, arg1, arg2,
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "StartedConnection", reflect.TypeOf((*MockConnectionTracer)(nil).StartedConnection), arg0, arg1, arg2, arg3, arg4)
 }
 
+// UpdatedCongestionState mocks base method
+func (m *MockConnectionTracer) UpdatedCongestionState(arg0 logging.CongestionState) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "UpdatedCongestionState", arg0)
+}
+
+// UpdatedCongestionState indicates an expected call of UpdatedCongestionState
+func (mr *MockConnectionTracerMockRecorder) UpdatedCongestionState(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "UpdatedCongestionState", reflect.TypeOf((*MockConnectionTracer)(nil).UpdatedCongestionState), arg0)
+}
+
 // UpdatedKey mocks base method
 func (m *MockConnectionTracer) UpdatedKey(arg0 protocol.KeyPhase, arg1 bool) {
 	m.ctrl.T.Helper()
diff --git a/logging/interface.go b/logging/interface.go
index 8db05b903..e9d4774e5 100644
--- a/logging/interface.go
+++ b/logging/interface.go
@@ -106,6 +106,7 @@ type ConnectionTracer interface {
 	DroppedPacket(PacketType, ByteCount, PacketDropReason)
 	UpdatedMetrics(rttStats *RTTStats, cwnd, bytesInFlight ByteCount, packetsInFlight int)
 	LostPacket(EncryptionLevel, PacketNumber, PacketLossReason)
+	UpdatedCongestionState(CongestionState)
 	UpdatedPTOCount(value uint32)
 	UpdatedKeyFromTLS(EncryptionLevel, Perspective)
 	UpdatedKey(generation KeyPhase, remote bool)
diff --git a/logging/mock_connection_tracer_test.go b/logging/mock_connection_tracer_test.go
index 8cba7d4cd..bf00e18cc 100644
--- a/logging/mock_connection_tracer_test.go
+++ b/logging/mock_connection_tracer_test.go
@@ -5,14 +5,13 @@
 package logging
 
 import (
-	"net"
-	"reflect"
-	"time"
-
-	"github.com/golang/mock/gomock"
-	"github.com/lucas-clemente/quic-go/internal/protocol"
-	"github.com/lucas-clemente/quic-go/internal/utils"
-	"github.com/lucas-clemente/quic-go/internal/wire"
+	gomock "github.com/golang/mock/gomock"
+	protocol "github.com/lucas-clemente/quic-go/internal/protocol"
+	utils "github.com/lucas-clemente/quic-go/internal/utils"
+	wire "github.com/lucas-clemente/quic-go/internal/wire"
+	net "net"
+	reflect "reflect"
+	time "time"
 )
 
 // MockConnectionTracer is a mock of ConnectionTracer interface
@@ -230,6 +229,18 @@ func (mr *MockConnectionTracerMockRecorder) StartedConnection(arg0, arg1, arg2,
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "StartedConnection", reflect.TypeOf((*MockConnectionTracer)(nil).StartedConnection), arg0, arg1, arg2, arg3, arg4)
 }
 
+// UpdatedCongestionState mocks base method
+func (m *MockConnectionTracer) UpdatedCongestionState(arg0 CongestionState) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "UpdatedCongestionState", arg0)
+}
+
+// UpdatedCongestionState indicates an expected call of UpdatedCongestionState
+func (mr *MockConnectionTracerMockRecorder) UpdatedCongestionState(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "UpdatedCongestionState", reflect.TypeOf((*MockConnectionTracer)(nil).UpdatedCongestionState), arg0)
+}
+
 // UpdatedKey mocks base method
 func (m *MockConnectionTracer) UpdatedKey(arg0 protocol.KeyPhase, arg1 bool) {
 	m.ctrl.T.Helper()
diff --git a/logging/multiplex.go b/logging/multiplex.go
index 1d20f3480..73e0c1286 100644
--- a/logging/multiplex.go
+++ b/logging/multiplex.go
@@ -120,6 +120,12 @@ func (m *connTracerMultiplexer) DroppedPacket(typ PacketType, size ByteCount, re
 	}
 }
 
+func (m *connTracerMultiplexer) UpdatedCongestionState(state CongestionState) {
+	for _, t := range m.tracers {
+		t.UpdatedCongestionState(state)
+	}
+}
+
 func (m *connTracerMultiplexer) UpdatedMetrics(rttStats *RTTStats, cwnd, bytesInFLight ByteCount, packetsInFlight int) {
 	for _, t := range m.tracers {
 		t.UpdatedMetrics(rttStats, cwnd, bytesInFLight, packetsInFlight)
diff --git a/logging/multiplex_test.go b/logging/multiplex_test.go
index 807a27750..dddb946f0 100644
--- a/logging/multiplex_test.go
+++ b/logging/multiplex_test.go
@@ -169,6 +169,12 @@ var _ = Describe("Tracing", func() {
 			tracer.DroppedPacket(PacketTypeInitial, 1337, PacketDropHeaderParseError)
 		})
 
+		It("traces the UpdatedCongestionState event", func() {
+			tr1.EXPECT().UpdatedCongestionState(CongestionStateRecovery)
+			tr2.EXPECT().UpdatedCongestionState(CongestionStateRecovery)
+			tracer.UpdatedCongestionState(CongestionStateRecovery)
+		})
+
 		It("traces the UpdatedMetrics event", func() {
 			rttStats := &RTTStats{}
 			rttStats.UpdateRTT(time.Second, 0, time.Now())
diff --git a/logging/types.go b/logging/types.go
index 3e0bfb4b1..41a776c89 100644
--- a/logging/types.go
+++ b/logging/types.go
@@ -81,3 +81,16 @@ const (
 	// This reason is not defined in the qlog draft, but very useful for debugging.
 	TimeoutReasonIdle
 )
+
+type CongestionState uint8
+
+const (
+	// CongestionStateSlowStart is the slow start phase of Reno / Cubic
+	CongestionStateSlowStart CongestionState = iota
+	// CongestionStateCongestionAvoidance is the slow start phase of Reno / Cubic
+	CongestionStateCongestionAvoidance
+	// CongestionStateCongestionAvoidance is the recovery phase of Reno / Cubic
+	CongestionStateRecovery
+	// CongestionStateApplicationLimited means that the congestion controller is application limited
+	CongestionStateApplicationLimited
+)
diff --git a/metrics/metrics.go b/metrics/metrics.go
index b0342557e..e151726f6 100644
--- a/metrics/metrics.go
+++ b/metrics/metrics.go
@@ -172,6 +172,7 @@ func (t *connTracer) ReceivedPacket(*logging.ExtendedHeader, logging.ByteCount,
 }
 func (t *connTracer) BufferedPacket(logging.PacketType)                                             {}
 func (t *connTracer) DroppedPacket(logging.PacketType, logging.ByteCount, logging.PacketDropReason) {}
+func (t *connTracer) UpdatedCongestionState(logging.CongestionState)                                {}
 func (t *connTracer) UpdatedMetrics(*logging.RTTStats, logging.ByteCount, logging.ByteCount, int)   {}
 func (t *connTracer) LostPacket(encLevel logging.EncryptionLevel, _ logging.PacketNumber, reason logging.PacketLossReason) {
 	stats.RecordWithTags(
diff --git a/qlog/qlog.go b/qlog/qlog.go
index 6ec2eff18..03107a775 100644
--- a/qlog/qlog.go
+++ b/qlog/qlog.go
@@ -316,6 +316,8 @@ func (t *connectionTracer) LostPacket(encLevel protocol.EncryptionLevel, pn prot
 	t.mutex.Unlock()
 }
 
+func (t *connectionTracer) UpdatedCongestionState(logging.CongestionState) {}
+
 func (t *connectionTracer) UpdatedPTOCount(value uint32) {
 	t.mutex.Lock()
 	t.recordEvent(time.Now(), &eventUpdatedPTO{Value: value})
diff --git a/session_test.go b/session_test.go
index 7a987a59f..bbadd556c 100644
--- a/session_test.go
+++ b/session_test.go
@@ -91,6 +91,7 @@ var _ = Describe("Session", func() {
 		tracer = mocks.NewMockConnectionTracer(mockCtrl)
 		tracer.EXPECT().SentTransportParameters(gomock.Any())
 		tracer.EXPECT().UpdatedKeyFromTLS(gomock.Any(), gomock.Any()).AnyTimes()
+		tracer.EXPECT().UpdatedCongestionState(gomock.Any())
 		sess = newSession(
 			mconn,
 			sessionRunner,
@@ -2154,6 +2155,7 @@ var _ = Describe("Client Session", func() {
 		tracer = mocks.NewMockConnectionTracer(mockCtrl)
 		tracer.EXPECT().SentTransportParameters(gomock.Any())
 		tracer.EXPECT().UpdatedKeyFromTLS(gomock.Any(), gomock.Any()).AnyTimes()
+		tracer.EXPECT().UpdatedCongestionState(gomock.Any())
 		sess = newClientSession(
 			mconn,
 			sessionRunner,