diff --git a/api/next/44886.txt b/api/next/44886.txt
new file mode 100644
index 0000000000..b3ab6996ea
--- /dev/null
+++ b/api/next/44886.txt
@@ -0,0 +1,41 @@
+pkg crypto/tls, const QUICEncryptionLevelApplication = 2 #44886
+pkg crypto/tls, const QUICEncryptionLevelApplication QUICEncryptionLevel #44886
+pkg crypto/tls, const QUICEncryptionLevelHandshake = 1 #44886
+pkg crypto/tls, const QUICEncryptionLevelHandshake QUICEncryptionLevel #44886
+pkg crypto/tls, const QUICEncryptionLevelInitial = 0 #44886
+pkg crypto/tls, const QUICEncryptionLevelInitial QUICEncryptionLevel #44886
+pkg crypto/tls, const QUICHandshakeDone = 6 #44886
+pkg crypto/tls, const QUICHandshakeDone QUICEventKind #44886
+pkg crypto/tls, const QUICNoEvent = 0 #44886
+pkg crypto/tls, const QUICNoEvent QUICEventKind #44886
+pkg crypto/tls, const QUICSetReadSecret = 1 #44886
+pkg crypto/tls, const QUICSetReadSecret QUICEventKind #44886
+pkg crypto/tls, const QUICSetWriteSecret = 2 #44886
+pkg crypto/tls, const QUICSetWriteSecret QUICEventKind #44886
+pkg crypto/tls, const QUICTransportParameters = 4 #44886
+pkg crypto/tls, const QUICTransportParameters QUICEventKind #44886
+pkg crypto/tls, const QUICTransportParametersRequired = 5 #44886
+pkg crypto/tls, const QUICTransportParametersRequired QUICEventKind #44886
+pkg crypto/tls, const QUICWriteData = 3 #44886
+pkg crypto/tls, const QUICWriteData QUICEventKind #44886
+pkg crypto/tls, func QUICClient(*QUICConfig) *QUICConn #44886
+pkg crypto/tls, func QUICServer(*QUICConfig) *QUICConn #44886
+pkg crypto/tls, method (*QUICConn) Close() error #44886
+pkg crypto/tls, method (*QUICConn) ConnectionState() ConnectionState #44886
+pkg crypto/tls, method (*QUICConn) HandleData(QUICEncryptionLevel, []uint8) error #44886
+pkg crypto/tls, method (*QUICConn) NextEvent() QUICEvent #44886
+pkg crypto/tls, method (*QUICConn) SetTransportParameters([]uint8) #44886
+pkg crypto/tls, method (*QUICConn) Start(context.Context) error #44886
+pkg crypto/tls, method (AlertError) Error() string #44886
+pkg crypto/tls, method (QUICEncryptionLevel) String() string #44886
+pkg crypto/tls, type AlertError uint8 #44886
+pkg crypto/tls, type QUICConfig struct #44886
+pkg crypto/tls, type QUICConfig struct, TLSConfig *Config #44886
+pkg crypto/tls, type QUICConn struct #44886
+pkg crypto/tls, type QUICEncryptionLevel int #44886
+pkg crypto/tls, type QUICEvent struct #44886
+pkg crypto/tls, type QUICEvent struct, Data []uint8 #44886
+pkg crypto/tls, type QUICEvent struct, Kind QUICEventKind #44886
+pkg crypto/tls, type QUICEvent struct, Level QUICEncryptionLevel #44886
+pkg crypto/tls, type QUICEvent struct, Suite uint16 #44886
+pkg crypto/tls, type QUICEventKind int #44886
diff --git a/src/crypto/tls/alert.go b/src/crypto/tls/alert.go
index 4790b73724..33022cd2b4 100644
--- a/src/crypto/tls/alert.go
+++ b/src/crypto/tls/alert.go
@@ -6,6 +6,16 @@ package tls
 
 import "strconv"
 
+// An AlertError is a TLS alert.
+//
+// When using a QUIC transport, QUICConn methods will return an error
+// which wraps AlertError rather than sending a TLS alert.
+type AlertError uint8
+
+func (e AlertError) Error() string {
+	return alert(e).String()
+}
+
 type alert uint8
 
 const (
diff --git a/src/crypto/tls/common.go b/src/crypto/tls/common.go
index 5394d64ac6..b8332e90fd 100644
--- a/src/crypto/tls/common.go
+++ b/src/crypto/tls/common.go
@@ -99,6 +99,7 @@ const (
 	extensionCertificateAuthorities  uint16 = 47
 	extensionSignatureAlgorithmsCert uint16 = 50
 	extensionKeyShare                uint16 = 51
+	extensionQUICTransportParameters uint16 = 57
 	extensionRenegotiationInfo       uint16 = 0xff01
 )
 
diff --git a/src/crypto/tls/conn.go b/src/crypto/tls/conn.go
index 847d3f8f06..e3607c8fec 100644
--- a/src/crypto/tls/conn.go
+++ b/src/crypto/tls/conn.go
@@ -29,6 +29,7 @@ type Conn struct {
 	conn        net.Conn
 	isClient    bool
 	handshakeFn func(context.Context) error // (*Conn).clientHandshake or serverHandshake
+	quic        *quicState                  // nil for non-QUIC connections
 
 	// isHandshakeComplete is true if the connection is currently transferring
 	// application data (i.e. is not currently processing a handshake).
@@ -176,7 +177,8 @@ type halfConn struct {
 	nextCipher any       // next encryption state
 	nextMac    hash.Hash // next MAC algorithm
 
-	trafficSecret []byte // current TLS 1.3 traffic secret
+	level         QUICEncryptionLevel // current QUIC encryption level
+	trafficSecret []byte              // current TLS 1.3 traffic secret
 }
 
 type permanentError struct {
@@ -221,8 +223,9 @@ func (hc *halfConn) changeCipherSpec() error {
 	return nil
 }
 
-func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, secret []byte) {
+func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, level QUICEncryptionLevel, secret []byte) {
 	hc.trafficSecret = secret
+	hc.level = level
 	key, iv := suite.trafficKey(secret)
 	hc.cipher = suite.aead(key, iv)
 	for i := range hc.seq {
@@ -613,6 +616,10 @@ func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error {
 	}
 	c.input.Reset(nil)
 
+	if c.quic != nil {
+		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with QUIC transport"))
+	}
+
 	// Read header, payload.
 	if err := c.readFromUntil(c.conn, recordHeaderLen); err != nil {
 		// RFC 8446, Section 6.1 suggests that EOF without an alertCloseNotify
@@ -702,6 +709,9 @@ func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error {
 		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
 
 	case recordTypeAlert:
+		if c.quic != nil {
+			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		}
 		if len(data) != 2 {
 			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
 		}
@@ -819,6 +829,10 @@ func (c *Conn) readFromUntil(r io.Reader, n int) error {
 
 // sendAlertLocked sends a TLS alert message.
 func (c *Conn) sendAlertLocked(err alert) error {
+	if c.quic != nil {
+		return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
+	}
+
 	switch err {
 	case alertNoRenegotiation, alertCloseNotify:
 		c.tmp[0] = alertLevelWarning
@@ -953,6 +967,19 @@ var outBufPool = sync.Pool{
 // writeRecordLocked writes a TLS record with the given type and payload to the
 // connection and updates the record layer state.
 func (c *Conn) writeRecordLocked(typ recordType, data []byte) (int, error) {
+	if c.quic != nil {
+		if typ != recordTypeHandshake {
+			return 0, errors.New("tls: internal error: sending non-handshake message to QUIC transport")
+		}
+		c.quicWriteCryptoData(c.out.level, data)
+		if !c.buffering {
+			if _, err := c.flush(); err != nil {
+				return 0, err
+			}
+		}
+		return len(data), nil
+	}
+
 	outBufPtr := outBufPool.Get().(*[]byte)
 	outBuf := *outBufPtr
 	defer func() {
@@ -1037,28 +1064,40 @@ func (c *Conn) writeChangeCipherRecord() error {
 	return err
 }
 
+// readHandshakeBytes reads handshake data until c.hand contains at least n bytes.
+func (c *Conn) readHandshakeBytes(n int) error {
+	if c.quic != nil {
+		return c.quicReadHandshakeBytes(n)
+	}
+	for c.hand.Len() < n {
+		if err := c.readRecord(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // readHandshake reads the next handshake message from
 // the record layer. If transcript is non-nil, the message
 // is written to the passed transcriptHash.
 func (c *Conn) readHandshake(transcript transcriptHash) (any, error) {
-	for c.hand.Len() < 4 {
-		if err := c.readRecord(); err != nil {
-			return nil, err
-		}
+	if err := c.readHandshakeBytes(4); err != nil {
+		return nil, err
 	}
-
 	data := c.hand.Bytes()
 	n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
 	if n > maxHandshake {
 		c.sendAlertLocked(alertInternalError)
 		return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake))
 	}
-	for c.hand.Len() < 4+n {
-		if err := c.readRecord(); err != nil {
-			return nil, err
-		}
+	if err := c.readHandshakeBytes(4 + n); err != nil {
+		return nil, err
 	}
 	data = c.hand.Next(4 + n)
+	return c.unmarshalHandshakeMessage(data, transcript)
+}
+
+func (c *Conn) unmarshalHandshakeMessage(data []byte, transcript transcriptHash) (handshakeMessage, error) {
 	var m handshakeMessage
 	switch data[0] {
 	case typeHelloRequest:
@@ -1249,7 +1288,6 @@ func (c *Conn) handlePostHandshakeMessage() error {
 	if err != nil {
 		return err
 	}
-
 	c.retryCount++
 	if c.retryCount > maxUselessRecords {
 		c.sendAlert(alertUnexpectedMessage)
@@ -1261,20 +1299,28 @@ func (c *Conn) handlePostHandshakeMessage() error {
 		return c.handleNewSessionTicket(msg)
 	case *keyUpdateMsg:
 		return c.handleKeyUpdate(msg)
-	default:
-		c.sendAlert(alertUnexpectedMessage)
-		return fmt.Errorf("tls: received unexpected handshake message of type %T", msg)
 	}
+	// The QUIC layer is supposed to treat an unexpected post-handshake CertificateRequest
+	// as a QUIC-level PROTOCOL_VIOLATION error (RFC 9001, Section 4.4). Returning an
+	// unexpected_message alert here doesn't provide it with enough information to distinguish
+	// this condition from other unexpected messages. This is probably fine.
+	c.sendAlert(alertUnexpectedMessage)
+	return fmt.Errorf("tls: received unexpected handshake message of type %T", msg)
 }
 
 func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error {
+	if c.quic != nil {
+		c.sendAlert(alertUnexpectedMessage)
+		return c.in.setErrorLocked(errors.New("tls: received unexpected key update message"))
+	}
+
 	cipherSuite := cipherSuiteTLS13ByID(c.cipherSuite)
 	if cipherSuite == nil {
 		return c.in.setErrorLocked(c.sendAlert(alertInternalError))
 	}
 
 	newSecret := cipherSuite.nextTrafficSecret(c.in.trafficSecret)
-	c.in.setTrafficSecret(cipherSuite, newSecret)
+	c.in.setTrafficSecret(cipherSuite, QUICEncryptionLevelInitial, newSecret)
 
 	if keyUpdate.updateRequested {
 		c.out.Lock()
@@ -1293,7 +1339,7 @@ func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error {
 		}
 
 		newSecret := cipherSuite.nextTrafficSecret(c.out.trafficSecret)
-		c.out.setTrafficSecret(cipherSuite, newSecret)
+		c.out.setTrafficSecret(cipherSuite, QUICEncryptionLevelInitial, newSecret)
 	}
 
 	return nil
@@ -1454,12 +1500,15 @@ func (c *Conn) handshakeContext(ctx context.Context) (ret error) {
 	// this cancellation. In the former case, we need to close the connection.
 	defer cancel()
 
-	// Start the "interrupter" goroutine, if this context might be canceled.
-	// (The background context cannot).
-	//
-	// The interrupter goroutine waits for the input context to be done and
-	// closes the connection if this happens before the function returns.
-	if ctx.Done() != nil {
+	if c.quic != nil {
+		c.quic.cancelc = handshakeCtx.Done()
+		c.quic.cancel = cancel
+	} else if ctx.Done() != nil {
+		// Start the "interrupter" goroutine, if this context might be canceled.
+		// (The background context cannot).
+		//
+		// The interrupter goroutine waits for the input context to be done and
+		// closes the connection if this happens before the function returns.
 		done := make(chan struct{})
 		interruptRes := make(chan error, 1)
 		defer func() {
@@ -1510,6 +1559,30 @@ func (c *Conn) handshakeContext(ctx context.Context) (ret error) {
 		panic("tls: internal error: handshake returned an error but is marked successful")
 	}
 
+	if c.quic != nil {
+		if c.handshakeErr == nil {
+			c.quicHandshakeComplete()
+			// Provide the 1-RTT read secret now that the handshake is complete.
+			// The QUIC layer MUST NOT decrypt 1-RTT packets prior to completing
+			// the handshake (RFC 9001, Section 5.7).
+			c.quicSetReadSecret(QUICEncryptionLevelApplication, c.cipherSuite, c.in.trafficSecret)
+		} else {
+			var a alert
+			c.out.Lock()
+			if !errors.As(c.out.err, &a) {
+				a = alertInternalError
+			}
+			c.out.Unlock()
+			// Return an error which wraps both the handshake error and
+			// any alert error we may have sent, or alertInternalError
+			// if we didn't send an alert.
+			// Truncate the text of the alert to 0 characters.
+			c.handshakeErr = fmt.Errorf("%w%.0w", c.handshakeErr, AlertError(a))
+		}
+		close(c.quic.blockedc)
+		close(c.quic.signalc)
+	}
+
 	return c.handshakeErr
 }
 
diff --git a/src/crypto/tls/handshake_client.go b/src/crypto/tls/handshake_client.go
index 63d86b9f3a..9f74cc4ef9 100644
--- a/src/crypto/tls/handshake_client.go
+++ b/src/crypto/tls/handshake_client.go
@@ -71,7 +71,6 @@ func (c *Conn) makeClientHello() (*clientHelloMsg, *ecdh.PrivateKey, error) {
 		vers:                         clientHelloVersion,
 		compressionMethods:           []uint8{compressionNone},
 		random:                       make([]byte, 32),
-		sessionId:                    make([]byte, 32),
 		ocspStapling:                 true,
 		scts:                         true,
 		serverName:                   hostnameInSNI(config.ServerName),
@@ -114,8 +113,13 @@ func (c *Conn) makeClientHello() (*clientHelloMsg, *ecdh.PrivateKey, error) {
 	// A random session ID is used to detect when the server accepted a ticket
 	// and is resuming a session (see RFC 5077). In TLS 1.3, it's always set as
 	// a compatibility measure (see RFC 8446, Section 4.1.2).
-	if _, err := io.ReadFull(config.rand(), hello.sessionId); err != nil {
-		return nil, nil, errors.New("tls: short read from Rand: " + err.Error())
+	//
+	// The session ID is not set for QUIC connections (see RFC 9001, Section 8.4).
+	if c.quic == nil {
+		hello.sessionId = make([]byte, 32)
+		if _, err := io.ReadFull(config.rand(), hello.sessionId); err != nil {
+			return nil, nil, errors.New("tls: short read from Rand: " + err.Error())
+		}
 	}
 
 	if hello.vers >= VersionTLS12 {
@@ -144,6 +148,17 @@ func (c *Conn) makeClientHello() (*clientHelloMsg, *ecdh.PrivateKey, error) {
 		hello.keyShares = []keyShare{{group: curveID, data: key.PublicKey().Bytes()}}
 	}
 
+	if c.quic != nil {
+		p, err := c.quicGetTransportParameters()
+		if err != nil {
+			return nil, nil, err
+		}
+		if p == nil {
+			p = []byte{}
+		}
+		hello.quicTransportParameters = p
+	}
+
 	return hello, key, nil
 }
 
@@ -271,7 +286,10 @@ func (c *Conn) loadSession(hello *clientHelloMsg) (cacheKey string,
 	}
 
 	// Try to resume a previously negotiated TLS session, if available.
-	cacheKey = clientSessionCacheKey(c.conn.RemoteAddr(), c.config)
+	cacheKey = c.clientSessionCacheKey()
+	if cacheKey == "" {
+		return "", nil, nil, nil, nil
+	}
 	session, ok := c.config.ClientSessionCache.Get(cacheKey)
 	if !ok || session == nil {
 		return cacheKey, nil, nil, nil, nil
@@ -722,7 +740,7 @@ func (hs *clientHandshakeState) processServerHello() (bool, error) {
 		}
 	}
 
-	if err := checkALPN(hs.hello.alpnProtocols, hs.serverHello.alpnProtocol); err != nil {
+	if err := checkALPN(hs.hello.alpnProtocols, hs.serverHello.alpnProtocol, false); err != nil {
 		c.sendAlert(alertUnsupportedExtension)
 		return false, err
 	}
@@ -760,8 +778,12 @@ func (hs *clientHandshakeState) processServerHello() (bool, error) {
 
 // checkALPN ensure that the server's choice of ALPN protocol is compatible with
 // the protocols that we advertised in the Client Hello.
-func checkALPN(clientProtos []string, serverProto string) error {
+func checkALPN(clientProtos []string, serverProto string, quic bool) error {
 	if serverProto == "" {
+		if quic && len(clientProtos) > 0 {
+			// RFC 9001, Section 8.1
+			return errors.New("tls: server did not select an ALPN protocol")
+		}
 		return nil
 	}
 	if len(clientProtos) == 0 {
@@ -1003,11 +1025,14 @@ func (c *Conn) getClientCertificate(cri *CertificateRequestInfo) (*Certificate,
 
 // clientSessionCacheKey returns a key used to cache sessionTickets that could
 // be used to resume previously negotiated TLS sessions with a server.
-func clientSessionCacheKey(serverAddr net.Addr, config *Config) string {
-	if len(config.ServerName) > 0 {
-		return config.ServerName
+func (c *Conn) clientSessionCacheKey() string {
+	if len(c.config.ServerName) > 0 {
+		return c.config.ServerName
 	}
-	return serverAddr.String()
+	if c.conn != nil {
+		return c.conn.RemoteAddr().String()
+	}
+	return ""
 }
 
 // hostnameInSNI converts name into an appropriate hostname for SNI.
diff --git a/src/crypto/tls/handshake_client_tls13.go b/src/crypto/tls/handshake_client_tls13.go
index 4a8661085e..15e0a74848 100644
--- a/src/crypto/tls/handshake_client_tls13.go
+++ b/src/crypto/tls/handshake_client_tls13.go
@@ -172,6 +172,9 @@ func (hs *clientHandshakeStateTLS13) checkServerHelloOrHRR() error {
 // sendDummyChangeCipherSpec sends a ChangeCipherSpec record for compatibility
 // with middleboxes that didn't implement TLS correctly. See RFC 8446, Appendix D.4.
 func (hs *clientHandshakeStateTLS13) sendDummyChangeCipherSpec() error {
+	if hs.c.quic != nil {
+		return nil
+	}
 	if hs.sentDummyCCS {
 		return nil
 	}
@@ -383,10 +386,18 @@ func (hs *clientHandshakeStateTLS13) establishHandshakeKeys() error {
 
 	clientSecret := hs.suite.deriveSecret(handshakeSecret,
 		clientHandshakeTrafficLabel, hs.transcript)
-	c.out.setTrafficSecret(hs.suite, clientSecret)
+	c.out.setTrafficSecret(hs.suite, QUICEncryptionLevelHandshake, clientSecret)
 	serverSecret := hs.suite.deriveSecret(handshakeSecret,
 		serverHandshakeTrafficLabel, hs.transcript)
-	c.in.setTrafficSecret(hs.suite, serverSecret)
+	c.in.setTrafficSecret(hs.suite, QUICEncryptionLevelHandshake, serverSecret)
+
+	if c.quic != nil {
+		if c.hand.Len() != 0 {
+			c.sendAlert(alertUnexpectedMessage)
+		}
+		c.quicSetWriteSecret(QUICEncryptionLevelHandshake, hs.suite.id, clientSecret)
+		c.quicSetReadSecret(QUICEncryptionLevelHandshake, hs.suite.id, serverSecret)
+	}
 
 	err = c.config.writeKeyLog(keyLogLabelClientHandshake, hs.hello.random, clientSecret)
 	if err != nil {
@@ -419,12 +430,30 @@ func (hs *clientHandshakeStateTLS13) readServerParameters() error {
 		return unexpectedMessageError(encryptedExtensions, msg)
 	}
 
-	if err := checkALPN(hs.hello.alpnProtocols, encryptedExtensions.alpnProtocol); err != nil {
-		c.sendAlert(alertUnsupportedExtension)
+	if err := checkALPN(hs.hello.alpnProtocols, encryptedExtensions.alpnProtocol, c.quic != nil); err != nil {
+		// RFC 8446 specifies that no_application_protocol is sent by servers, but
+		// does not specify how clients handle the selection of an incompatible protocol.
+		// RFC 9001 Section 8.1 specifies that QUIC clients send no_application_protocol
+		// in this case. Always sending no_application_protocol seems reasonable.
+		c.sendAlert(alertNoApplicationProtocol)
 		return err
 	}
 	c.clientProtocol = encryptedExtensions.alpnProtocol
 
+	if c.quic != nil {
+		if encryptedExtensions.quicTransportParameters == nil {
+			// RFC 9001 Section 8.2.
+			c.sendAlert(alertMissingExtension)
+			return errors.New("tls: server did not send a quic_transport_parameters extension")
+		}
+		c.quicSetTransportParameters(encryptedExtensions.quicTransportParameters)
+	} else {
+		if encryptedExtensions.quicTransportParameters != nil {
+			c.sendAlert(alertUnsupportedExtension)
+			return errors.New("tls: server sent an unexpected quic_transport_parameters extension")
+		}
+	}
+
 	return nil
 }
 
@@ -552,7 +581,7 @@ func (hs *clientHandshakeStateTLS13) readServerFinished() error {
 		clientApplicationTrafficLabel, hs.transcript)
 	serverSecret := hs.suite.deriveSecret(hs.masterSecret,
 		serverApplicationTrafficLabel, hs.transcript)
-	c.in.setTrafficSecret(hs.suite, serverSecret)
+	c.in.setTrafficSecret(hs.suite, QUICEncryptionLevelApplication, serverSecret)
 
 	err = c.config.writeKeyLog(keyLogLabelClientTraffic, hs.hello.random, hs.trafficSecret)
 	if err != nil {
@@ -648,13 +677,20 @@ func (hs *clientHandshakeStateTLS13) sendClientFinished() error {
 		return err
 	}
 
-	c.out.setTrafficSecret(hs.suite, hs.trafficSecret)
+	c.out.setTrafficSecret(hs.suite, QUICEncryptionLevelApplication, hs.trafficSecret)
 
 	if !c.config.SessionTicketsDisabled && c.config.ClientSessionCache != nil {
 		c.resumptionSecret = hs.suite.deriveSecret(hs.masterSecret,
 			resumptionLabel, hs.transcript)
 	}
 
+	if c.quic != nil {
+		if c.hand.Len() != 0 {
+			c.sendAlert(alertUnexpectedMessage)
+		}
+		c.quicSetWriteSecret(QUICEncryptionLevelApplication, hs.suite.id, hs.trafficSecret)
+	}
+
 	return nil
 }
 
@@ -702,8 +738,10 @@ func (c *Conn) handleNewSessionTicket(msg *newSessionTicketMsgTLS13) error {
 		scts:               c.scts,
 	}
 
-	cacheKey := clientSessionCacheKey(c.conn.RemoteAddr(), c.config)
-	c.config.ClientSessionCache.Put(cacheKey, session)
+	cacheKey := c.clientSessionCacheKey()
+	if cacheKey != "" {
+		c.config.ClientSessionCache.Put(cacheKey, session)
+	}
 
 	return nil
 }
diff --git a/src/crypto/tls/handshake_messages.go b/src/crypto/tls/handshake_messages.go
index 695aacf126..eac01fd085 100644
--- a/src/crypto/tls/handshake_messages.go
+++ b/src/crypto/tls/handshake_messages.go
@@ -93,6 +93,7 @@ type clientHelloMsg struct {
 	pskModes                         []uint8
 	pskIdentities                    []pskIdentity
 	pskBinders                       [][]byte
+	quicTransportParameters          []byte
 }
 
 func (m *clientHelloMsg) marshal() ([]byte, error) {
@@ -246,6 +247,13 @@ func (m *clientHelloMsg) marshal() ([]byte, error) {
 			})
 		})
 	}
+	if m.quicTransportParameters != nil { // marshal zero-length parameters when present
+		// RFC 9001, Section 8.2
+		exts.AddUint16(extensionQUICTransportParameters)
+		exts.AddUint16LengthPrefixed(func(exts *cryptobyte.Builder) {
+			exts.AddBytes(m.quicTransportParameters)
+		})
+	}
 	if len(m.pskIdentities) > 0 { // pre_shared_key must be the last extension
 		// RFC 8446, Section 4.2.11
 		exts.AddUint16(extensionPreSharedKey)
@@ -560,6 +568,11 @@ func (m *clientHelloMsg) unmarshal(data []byte) bool {
 			if !readUint8LengthPrefixed(&extData, &m.pskModes) {
 				return false
 			}
+		case extensionQUICTransportParameters:
+			m.quicTransportParameters = make([]byte, len(extData))
+			if !extData.CopyBytes(m.quicTransportParameters) {
+				return false
+			}
 		case extensionPreSharedKey:
 			// RFC 8446, Section 4.2.11
 			if !extensions.Empty() {
@@ -860,8 +873,9 @@ func (m *serverHelloMsg) unmarshal(data []byte) bool {
 }
 
 type encryptedExtensionsMsg struct {
-	raw          []byte
-	alpnProtocol string
+	raw                     []byte
+	alpnProtocol            string
+	quicTransportParameters []byte
 }
 
 func (m *encryptedExtensionsMsg) marshal() ([]byte, error) {
@@ -883,6 +897,13 @@ func (m *encryptedExtensionsMsg) marshal() ([]byte, error) {
 					})
 				})
 			}
+			if m.quicTransportParameters != nil { // marshal zero-length parameters when present
+				// draft-ietf-quic-tls-32, Section 8.2
+				b.AddUint16(extensionQUICTransportParameters)
+				b.AddUint16LengthPrefixed(func(b *cryptobyte.Builder) {
+					b.AddBytes(m.quicTransportParameters)
+				})
+			}
 		})
 	})
 
@@ -921,6 +942,11 @@ func (m *encryptedExtensionsMsg) unmarshal(data []byte) bool {
 				return false
 			}
 			m.alpnProtocol = string(proto)
+		case extensionQUICTransportParameters:
+			m.quicTransportParameters = make([]byte, len(extData))
+			if !extData.CopyBytes(m.quicTransportParameters) {
+				return false
+			}
 		default:
 			// Ignore unknown extensions.
 			continue
diff --git a/src/crypto/tls/handshake_messages_test.go b/src/crypto/tls/handshake_messages_test.go
index 206e2fb024..1ef6c432ff 100644
--- a/src/crypto/tls/handshake_messages_test.go
+++ b/src/crypto/tls/handshake_messages_test.go
@@ -197,6 +197,9 @@ func (*clientHelloMsg) Generate(rand *rand.Rand, size int) reflect.Value {
 		m.pskIdentities = append(m.pskIdentities, psk)
 		m.pskBinders = append(m.pskBinders, randomBytes(rand.Intn(50)+32, rand))
 	}
+	if rand.Intn(10) > 5 {
+		m.quicTransportParameters = randomBytes(rand.Intn(500), rand)
+	}
 	if rand.Intn(10) > 5 {
 		m.earlyData = true
 	}
diff --git a/src/crypto/tls/handshake_server.go b/src/crypto/tls/handshake_server.go
index a17ba2fe27..450c5f7714 100644
--- a/src/crypto/tls/handshake_server.go
+++ b/src/crypto/tls/handshake_server.go
@@ -218,7 +218,7 @@ func (hs *serverHandshakeState) processClientHello() error {
 		c.serverName = hs.clientHello.serverName
 	}
 
-	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols)
+	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols, false)
 	if err != nil {
 		c.sendAlert(alertNoApplicationProtocol)
 		return err
@@ -279,8 +279,12 @@ func (hs *serverHandshakeState) processClientHello() error {
 // negotiateALPN picks a shared ALPN protocol that both sides support in server
 // preference order. If ALPN is not configured or the peer doesn't support it,
 // it returns "" and no error.
-func negotiateALPN(serverProtos, clientProtos []string) (string, error) {
+func negotiateALPN(serverProtos, clientProtos []string, quic bool) (string, error) {
 	if len(serverProtos) == 0 || len(clientProtos) == 0 {
+		if quic && len(serverProtos) != 0 {
+			// RFC 9001, Section 8.1
+			return "", fmt.Errorf("tls: client did not request an application protocol")
+		}
 		return "", nil
 	}
 	var http11fallback bool
diff --git a/src/crypto/tls/handshake_server_tls13.go b/src/crypto/tls/handshake_server_tls13.go
index b7b568cd84..69ebe1c7d5 100644
--- a/src/crypto/tls/handshake_server_tls13.go
+++ b/src/crypto/tls/handshake_server_tls13.go
@@ -226,6 +226,20 @@ GroupSelection:
 		return errors.New("tls: invalid client key share")
 	}
 
+	if c.quic != nil {
+		if hs.clientHello.quicTransportParameters == nil {
+			// RFC 9001 Section 8.2.
+			c.sendAlert(alertMissingExtension)
+			return errors.New("tls: client did not send a quic_transport_parameters extension")
+		}
+		c.quicSetTransportParameters(hs.clientHello.quicTransportParameters)
+	} else {
+		if hs.clientHello.quicTransportParameters != nil {
+			c.sendAlert(alertUnsupportedExtension)
+			return errors.New("tls: client sent an unexpected quic_transport_parameters extension")
+		}
+	}
+
 	c.serverName = hs.clientHello.serverName
 	return nil
 }
@@ -397,6 +411,9 @@ func (hs *serverHandshakeStateTLS13) pickCertificate() error {
 // sendDummyChangeCipherSpec sends a ChangeCipherSpec record for compatibility
 // with middleboxes that didn't implement TLS correctly. See RFC 8446, Appendix D.4.
 func (hs *serverHandshakeStateTLS13) sendDummyChangeCipherSpec() error {
+	if hs.c.quic != nil {
+		return nil
+	}
 	if hs.sentDummyCCS {
 		return nil
 	}
@@ -548,10 +565,18 @@ func (hs *serverHandshakeStateTLS13) sendServerParameters() error {
 
 	clientSecret := hs.suite.deriveSecret(hs.handshakeSecret,
 		clientHandshakeTrafficLabel, hs.transcript)
-	c.in.setTrafficSecret(hs.suite, clientSecret)
+	c.in.setTrafficSecret(hs.suite, QUICEncryptionLevelHandshake, clientSecret)
 	serverSecret := hs.suite.deriveSecret(hs.handshakeSecret,
 		serverHandshakeTrafficLabel, hs.transcript)
-	c.out.setTrafficSecret(hs.suite, serverSecret)
+	c.out.setTrafficSecret(hs.suite, QUICEncryptionLevelHandshake, serverSecret)
+
+	if c.quic != nil {
+		if c.hand.Len() != 0 {
+			c.sendAlert(alertUnexpectedMessage)
+		}
+		c.quicSetWriteSecret(QUICEncryptionLevelHandshake, hs.suite.id, serverSecret)
+		c.quicSetReadSecret(QUICEncryptionLevelHandshake, hs.suite.id, clientSecret)
+	}
 
 	err := c.config.writeKeyLog(keyLogLabelClientHandshake, hs.clientHello.random, clientSecret)
 	if err != nil {
@@ -566,7 +591,7 @@ func (hs *serverHandshakeStateTLS13) sendServerParameters() error {
 
 	encryptedExtensions := new(encryptedExtensionsMsg)
 
-	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols)
+	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols, c.quic != nil)
 	if err != nil {
 		c.sendAlert(alertNoApplicationProtocol)
 		return err
@@ -574,6 +599,14 @@ func (hs *serverHandshakeStateTLS13) sendServerParameters() error {
 	encryptedExtensions.alpnProtocol = selectedProto
 	c.clientProtocol = selectedProto
 
+	if c.quic != nil {
+		p, err := c.quicGetTransportParameters()
+		if err != nil {
+			return err
+		}
+		encryptedExtensions.quicTransportParameters = p
+	}
+
 	if _, err := hs.c.writeHandshakeRecord(encryptedExtensions, hs.transcript); err != nil {
 		return err
 	}
@@ -672,7 +705,15 @@ func (hs *serverHandshakeStateTLS13) sendServerFinished() error {
 		clientApplicationTrafficLabel, hs.transcript)
 	serverSecret := hs.suite.deriveSecret(hs.masterSecret,
 		serverApplicationTrafficLabel, hs.transcript)
-	c.out.setTrafficSecret(hs.suite, serverSecret)
+	c.out.setTrafficSecret(hs.suite, QUICEncryptionLevelApplication, serverSecret)
+
+	if c.quic != nil {
+		if c.hand.Len() != 0 {
+			// TODO: Handle this in setTrafficSecret?
+			c.sendAlert(alertUnexpectedMessage)
+		}
+		c.quicSetWriteSecret(QUICEncryptionLevelApplication, hs.suite.id, serverSecret)
+	}
 
 	err := c.config.writeKeyLog(keyLogLabelClientTraffic, hs.clientHello.random, hs.trafficSecret)
 	if err != nil {
@@ -887,7 +928,7 @@ func (hs *serverHandshakeStateTLS13) readClientFinished() error {
 		return errors.New("tls: invalid client finished hash")
 	}
 
-	c.in.setTrafficSecret(hs.suite, hs.trafficSecret)
+	c.in.setTrafficSecret(hs.suite, QUICEncryptionLevelApplication, hs.trafficSecret)
 
 	return nil
 }
diff --git a/src/crypto/tls/quic.go b/src/crypto/tls/quic.go
new file mode 100644
index 0000000000..a59b893738
--- /dev/null
+++ b/src/crypto/tls/quic.go
@@ -0,0 +1,376 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+import (
+	"context"
+	"errors"
+	"fmt"
+)
+
+// QUICEncryptionLevel represents a QUIC encryption level used to transmit
+// handshake messages.
+type QUICEncryptionLevel int
+
+const (
+	QUICEncryptionLevelInitial = QUICEncryptionLevel(iota)
+	QUICEncryptionLevelHandshake
+	QUICEncryptionLevelApplication
+)
+
+func (l QUICEncryptionLevel) String() string {
+	switch l {
+	case QUICEncryptionLevelInitial:
+		return "Initial"
+	case QUICEncryptionLevelHandshake:
+		return "Handshake"
+	case QUICEncryptionLevelApplication:
+		return "Application"
+	default:
+		return fmt.Sprintf("QUICEncryptionLevel(%v)", int(l))
+	}
+}
+
+// A QUICConn represents a connection which uses a QUIC implementation as the underlying
+// transport as described in RFC 9001.
+//
+// Methods of QUICConn are not safe for concurrent use.
+type QUICConn struct {
+	conn *Conn
+}
+
+// A QUICConfig configures a QUICConn.
+type QUICConfig struct {
+	TLSConfig *Config
+}
+
+// A QUICEventKind is a type of operation on a QUIC connection.
+type QUICEventKind int
+
+const (
+	// QUICNoEvent indicates that there are no events available.
+	QUICNoEvent QUICEventKind = iota
+
+	// QUICSetReadSecret and QUICSetWriteSecret provide the read and write
+	// secrets for a given encryption level.
+	// QUICEvent.Level, QUICEvent.Data, and QUICEvent.Suite are set.
+	//
+	// Secrets for the Initial encryption level are derived from the initial
+	// destination connection ID, and are not provided by the QUICConn.
+	QUICSetReadSecret
+	QUICSetWriteSecret
+
+	// QUICWriteData provides data to send to the peer in CRYPTO frames.
+	// QUICEvent.Data is set.
+	QUICWriteData
+
+	// QUICTransportParameters provides the peer's QUIC transport parameters.
+	// QUICEvent.Data is set.
+	QUICTransportParameters
+
+	// QUICTransportParametersRequired indicates that the caller must provide
+	// QUIC transport parameters to send to the peer. The caller should set
+	// the transport parameters with QUICConn.SetTransportParameters and call
+	// QUICConn.NextEvent again.
+	//
+	// If transport parameters are set before calling QUICConn.Start, the
+	// connection will never generate a QUICTransportParametersRequired event.
+	QUICTransportParametersRequired
+
+	// QUICHandshakeDone indicates that the TLS handshake has completed.
+	QUICHandshakeDone
+)
+
+// A QUICEvent is an event occurring on a QUIC connection.
+//
+// The type of event is specified by the Kind field.
+// The contents of the other fields are kind-specific.
+type QUICEvent struct {
+	Kind QUICEventKind
+
+	// Set for QUICSetReadSecret, QUICSetWriteSecret, and QUICWriteData.
+	Level QUICEncryptionLevel
+
+	// Set for QUICTransportParameters, QUICSetReadSecret, QUICSetWriteSecret, and QUICWriteData.
+	// The contents are owned by crypto/tls, and are valid until the next NextEvent call.
+	Data []byte
+
+	// Set for QUICSetReadSecret and QUICSetWriteSecret.
+	Suite uint16
+}
+
+type quicState struct {
+	events    []QUICEvent
+	nextEvent int
+
+	// eventArr is a statically allocated event array, large enough to handle
+	// the usual maximum number of events resulting from a single call:
+	// transport parameters, Initial data, Handshake write and read secrets,
+	// Handshake data, Application write secret, Application data.
+	eventArr [7]QUICEvent
+
+	started  bool
+	signalc  chan struct{}   // handshake data is available to be read
+	blockedc chan struct{}   // handshake is waiting for data, closed when done
+	cancelc  <-chan struct{} // handshake has been canceled
+	cancel   context.CancelFunc
+
+	// readbuf is shared between HandleData and the handshake goroutine.
+	// HandshakeCryptoData passes ownership to the handshake goroutine by
+	// reading from signalc, and reclaims ownership by reading from blockedc.
+	readbuf []byte
+
+	transportParams []byte // to send to the peer
+}
+
+// QUICClient returns a new TLS client side connection using QUICTransport as the
+// underlying transport. The config cannot be nil.
+//
+// The config's MinVersion must be at least TLS 1.3.
+func QUICClient(config *QUICConfig) *QUICConn {
+	return newQUICConn(Client(nil, config.TLSConfig))
+}
+
+// QUICServer returns a new TLS server side connection using QUICTransport as the
+// underlying transport. The config cannot be nil.
+//
+// The config's MinVersion must be at least TLS 1.3.
+func QUICServer(config *QUICConfig) *QUICConn {
+	return newQUICConn(Server(nil, config.TLSConfig))
+}
+
+func newQUICConn(conn *Conn) *QUICConn {
+	conn.quic = &quicState{
+		signalc:  make(chan struct{}),
+		blockedc: make(chan struct{}),
+	}
+	conn.quic.events = conn.quic.eventArr[:0]
+	return &QUICConn{
+		conn: conn,
+	}
+}
+
+// Start starts the client or server handshake protocol.
+// It may produce connection events, which may be read with NextEvent.
+//
+// Start must be called at most once.
+func (q *QUICConn) Start(ctx context.Context) error {
+	if q.conn.quic.started {
+		return quicError(errors.New("tls: Start called more than once"))
+	}
+	q.conn.quic.started = true
+	if q.conn.config.MinVersion < VersionTLS13 {
+		return quicError(errors.New("tls: Config MinVersion must be at least TLS 1.13"))
+	}
+	go q.conn.HandshakeContext(ctx)
+	if _, ok := <-q.conn.quic.blockedc; !ok {
+		return q.conn.handshakeErr
+	}
+	return nil
+}
+
+// NextEvent returns the next event occurring on the connection.
+// It returns an event with a Kind of QUICNoEvent when no events are available.
+func (q *QUICConn) NextEvent() QUICEvent {
+	qs := q.conn.quic
+	if last := qs.nextEvent - 1; last >= 0 && len(qs.events[last].Data) > 0 {
+		// Write over some of the previous event's data,
+		// to catch callers erroniously retaining it.
+		qs.events[last].Data[0] = 0
+	}
+	if qs.nextEvent >= len(qs.events) {
+		qs.events = qs.events[:0]
+		qs.nextEvent = 0
+		return QUICEvent{Kind: QUICNoEvent}
+	}
+	e := qs.events[qs.nextEvent]
+	qs.events[qs.nextEvent] = QUICEvent{} // zero out references to data
+	qs.nextEvent++
+	return e
+}
+
+// Close closes the connection and stops any in-progress handshake.
+func (q *QUICConn) Close() error {
+	if q.conn.quic.cancel == nil {
+		return nil // never started
+	}
+	q.conn.quic.cancel()
+	for range q.conn.quic.blockedc {
+		// Wait for the handshake goroutine to return.
+	}
+	return q.conn.handshakeErr
+}
+
+// HandleData handles handshake bytes received from the peer.
+// It may produce connection events, which may be read with NextEvent.
+func (q *QUICConn) HandleData(level QUICEncryptionLevel, data []byte) error {
+	c := q.conn
+	if c.in.level != level {
+		return quicError(c.in.setErrorLocked(errors.New("tls: handshake data received at wrong level")))
+	}
+	c.quic.readbuf = data
+	<-c.quic.signalc
+	_, ok := <-c.quic.blockedc
+	if ok {
+		// The handshake goroutine is waiting for more data.
+		return nil
+	}
+	// The handshake goroutine has exited.
+	c.hand.Write(c.quic.readbuf)
+	c.quic.readbuf = nil
+	for q.conn.hand.Len() >= 4 && q.conn.handshakeErr == nil {
+		b := q.conn.hand.Bytes()
+		n := int(b[1])<<16 | int(b[2])<<8 | int(b[3])
+		if 4+n < len(b) {
+			return nil
+		}
+		if err := q.conn.handlePostHandshakeMessage(); err != nil {
+			return quicError(err)
+		}
+	}
+	if q.conn.handshakeErr != nil {
+		return quicError(q.conn.handshakeErr)
+	}
+	return nil
+}
+
+// ConnectionState returns basic TLS details about the connection.
+func (q *QUICConn) ConnectionState() ConnectionState {
+	return q.conn.ConnectionState()
+}
+
+// SetTransportParameters sets the transport parameters to send to the peer.
+//
+// Server connections may delay setting the transport parameters until after
+// receiving the client's transport parameters. See QUICTransportParametersRequired.
+func (q *QUICConn) SetTransportParameters(params []byte) {
+	if params == nil {
+		params = []byte{}
+	}
+	q.conn.quic.transportParams = params
+	if q.conn.quic.started {
+		<-q.conn.quic.signalc
+		<-q.conn.quic.blockedc
+	}
+}
+
+// quicError ensures err is an AlertError.
+// If err is not already, quicError wraps it with alertInternalError.
+func quicError(err error) error {
+	if err == nil {
+		return nil
+	}
+	var ae AlertError
+	if errors.As(err, &ae) {
+		return err
+	}
+	var a alert
+	if !errors.As(err, &a) {
+		a = alertInternalError
+	}
+	// Return an error wrapping the original error and an AlertError.
+	// Truncate the text of the alert to 0 characters.
+	return fmt.Errorf("%w%.0w", err, AlertError(a))
+}
+
+func (c *Conn) quicReadHandshakeBytes(n int) error {
+	for c.hand.Len() < n {
+		if err := c.quicWaitForSignal(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (c *Conn) quicSetReadSecret(level QUICEncryptionLevel, suite uint16, secret []byte) {
+	c.quic.events = append(c.quic.events, QUICEvent{
+		Kind:  QUICSetReadSecret,
+		Level: level,
+		Suite: suite,
+		Data:  secret,
+	})
+}
+
+func (c *Conn) quicSetWriteSecret(level QUICEncryptionLevel, suite uint16, secret []byte) {
+	c.quic.events = append(c.quic.events, QUICEvent{
+		Kind:  QUICSetWriteSecret,
+		Level: level,
+		Suite: suite,
+		Data:  secret,
+	})
+}
+
+func (c *Conn) quicWriteCryptoData(level QUICEncryptionLevel, data []byte) {
+	var last *QUICEvent
+	if len(c.quic.events) > 0 {
+		last = &c.quic.events[len(c.quic.events)-1]
+	}
+	if last == nil || last.Kind != QUICWriteData || last.Level != level {
+		c.quic.events = append(c.quic.events, QUICEvent{
+			Kind:  QUICWriteData,
+			Level: level,
+		})
+		last = &c.quic.events[len(c.quic.events)-1]
+	}
+	last.Data = append(last.Data, data...)
+}
+
+func (c *Conn) quicSetTransportParameters(params []byte) {
+	c.quic.events = append(c.quic.events, QUICEvent{
+		Kind: QUICTransportParameters,
+		Data: params,
+	})
+}
+
+func (c *Conn) quicGetTransportParameters() ([]byte, error) {
+	if c.quic.transportParams == nil {
+		c.quic.events = append(c.quic.events, QUICEvent{
+			Kind: QUICTransportParametersRequired,
+		})
+	}
+	for c.quic.transportParams == nil {
+		if err := c.quicWaitForSignal(); err != nil {
+			return nil, err
+		}
+	}
+	return c.quic.transportParams, nil
+}
+
+func (c *Conn) quicHandshakeComplete() {
+	c.quic.events = append(c.quic.events, QUICEvent{
+		Kind: QUICHandshakeDone,
+	})
+}
+
+// quicWaitForSignal notifies the QUICConn that handshake progress is blocked,
+// and waits for a signal that the handshake should proceed.
+//
+// The handshake may become blocked waiting for handshake bytes
+// or for the user to provide transport parameters.
+func (c *Conn) quicWaitForSignal() error {
+	// Drop the handshake mutex while blocked to allow the user
+	// to call ConnectionState before the handshake completes.
+	c.handshakeMutex.Unlock()
+	defer c.handshakeMutex.Lock()
+	// Send on blockedc to notify the QUICConn that the handshake is blocked.
+	// Exported methods of QUICConn wait for the handshake to become blocked
+	// before returning to the user.
+	select {
+	case c.quic.blockedc <- struct{}{}:
+	case <-c.quic.cancelc:
+		return c.sendAlertLocked(alertCloseNotify)
+	}
+	// The QUICConn reads from signalc to notify us that the handshake may
+	// be able to proceed. (The QUICConn reads, because we close signalc to
+	// indicate that the handshake has completed.)
+	select {
+	case c.quic.signalc <- struct{}{}:
+		c.hand.Write(c.quic.readbuf)
+		c.quic.readbuf = nil
+	case <-c.quic.cancelc:
+		return c.sendAlertLocked(alertCloseNotify)
+	}
+	return nil
+}
diff --git a/src/crypto/tls/quic_test.go b/src/crypto/tls/quic_test.go
new file mode 100644
index 0000000000..58054de80d
--- /dev/null
+++ b/src/crypto/tls/quic_test.go
@@ -0,0 +1,430 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+import (
+	"context"
+	"errors"
+	"reflect"
+	"testing"
+)
+
+type testQUICConn struct {
+	t           *testing.T
+	conn        *QUICConn
+	readSecret  map[QUICEncryptionLevel]suiteSecret
+	writeSecret map[QUICEncryptionLevel]suiteSecret
+	gotParams   []byte
+	complete    bool
+}
+
+func newTestQUICClient(t *testing.T, config *Config) *testQUICConn {
+	q := &testQUICConn{t: t}
+	q.conn = QUICClient(&QUICConfig{
+		TLSConfig: config,
+	})
+	t.Cleanup(func() {
+		q.conn.Close()
+	})
+	return q
+}
+
+func newTestQUICServer(t *testing.T, config *Config) *testQUICConn {
+	q := &testQUICConn{t: t}
+	q.conn = QUICServer(&QUICConfig{
+		TLSConfig: config,
+	})
+	t.Cleanup(func() {
+		q.conn.Close()
+	})
+	return q
+}
+
+type suiteSecret struct {
+	suite  uint16
+	secret []byte
+}
+
+func (q *testQUICConn) setReadSecret(level QUICEncryptionLevel, suite uint16, secret []byte) {
+	if _, ok := q.writeSecret[level]; !ok {
+		q.t.Errorf("SetReadSecret for level %v called before SetWriteSecret", level)
+	}
+	if level == QUICEncryptionLevelApplication && !q.complete {
+		q.t.Errorf("SetReadSecret for level %v called before HandshakeComplete", level)
+	}
+	if _, ok := q.readSecret[level]; ok {
+		q.t.Errorf("SetReadSecret for level %v called twice", level)
+	}
+	if q.readSecret == nil {
+		q.readSecret = map[QUICEncryptionLevel]suiteSecret{}
+	}
+	switch level {
+	case QUICEncryptionLevelHandshake, QUICEncryptionLevelApplication:
+		q.readSecret[level] = suiteSecret{suite, secret}
+	default:
+		q.t.Errorf("SetReadSecret for unexpected level %v", level)
+	}
+}
+
+func (q *testQUICConn) setWriteSecret(level QUICEncryptionLevel, suite uint16, secret []byte) {
+	if _, ok := q.writeSecret[level]; ok {
+		q.t.Errorf("SetWriteSecret for level %v called twice", level)
+	}
+	if q.writeSecret == nil {
+		q.writeSecret = map[QUICEncryptionLevel]suiteSecret{}
+	}
+	switch level {
+	case QUICEncryptionLevelHandshake, QUICEncryptionLevelApplication:
+		q.writeSecret[level] = suiteSecret{suite, secret}
+	default:
+		q.t.Errorf("SetWriteSecret for unexpected level %v", level)
+	}
+}
+
+var errTransportParametersRequired = errors.New("transport parameters required")
+
+func runTestQUICConnection(ctx context.Context, a, b *testQUICConn, onHandleCryptoData func()) error {
+	for _, c := range []*testQUICConn{a, b} {
+		if !c.conn.conn.quic.started {
+			if err := c.conn.Start(ctx); err != nil {
+				return err
+			}
+		}
+	}
+	idleCount := 0
+	for {
+		e := a.conn.NextEvent()
+		switch e.Kind {
+		case QUICNoEvent:
+			idleCount++
+			if idleCount == 2 {
+				if !a.complete || !b.complete {
+					return errors.New("handshake incomplete")
+				}
+				return nil
+			}
+			a, b = b, a
+		case QUICSetReadSecret:
+			a.setReadSecret(e.Level, e.Suite, e.Data)
+		case QUICSetWriteSecret:
+			a.setWriteSecret(e.Level, e.Suite, e.Data)
+		case QUICWriteData:
+			if err := b.conn.HandleData(e.Level, e.Data); err != nil {
+				return err
+			}
+		case QUICTransportParameters:
+			a.gotParams = e.Data
+			if a.gotParams == nil {
+				a.gotParams = []byte{}
+			}
+		case QUICTransportParametersRequired:
+			return errTransportParametersRequired
+		case QUICHandshakeDone:
+			a.complete = true
+		}
+		if e.Kind != QUICNoEvent {
+			idleCount = 0
+		}
+	}
+}
+
+func TestQUICConnection(t *testing.T) {
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+
+	cli := newTestQUICClient(t, config)
+	cli.conn.SetTransportParameters(nil)
+
+	srv := newTestQUICServer(t, config)
+	srv.conn.SetTransportParameters(nil)
+
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != nil {
+		t.Fatalf("error during connection handshake: %v", err)
+	}
+
+	if _, ok := cli.readSecret[QUICEncryptionLevelHandshake]; !ok {
+		t.Errorf("client has no Handshake secret")
+	}
+	if _, ok := cli.readSecret[QUICEncryptionLevelApplication]; !ok {
+		t.Errorf("client has no Application secret")
+	}
+	if _, ok := srv.readSecret[QUICEncryptionLevelHandshake]; !ok {
+		t.Errorf("server has no Handshake secret")
+	}
+	if _, ok := srv.readSecret[QUICEncryptionLevelApplication]; !ok {
+		t.Errorf("server has no Application secret")
+	}
+	for _, level := range []QUICEncryptionLevel{QUICEncryptionLevelHandshake, QUICEncryptionLevelApplication} {
+		if _, ok := cli.readSecret[level]; !ok {
+			t.Errorf("client has no %v read secret", level)
+		}
+		if _, ok := srv.readSecret[level]; !ok {
+			t.Errorf("server has no %v read secret", level)
+		}
+		if !reflect.DeepEqual(cli.readSecret[level], srv.writeSecret[level]) {
+			t.Errorf("client read secret does not match server write secret for level %v", level)
+		}
+		if !reflect.DeepEqual(cli.writeSecret[level], srv.readSecret[level]) {
+			t.Errorf("client write secret does not match server read secret for level %v", level)
+		}
+	}
+}
+
+func TestQUICSessionResumption(t *testing.T) {
+	clientConfig := testConfig.Clone()
+	clientConfig.MinVersion = VersionTLS13
+	clientConfig.ClientSessionCache = NewLRUClientSessionCache(1)
+	clientConfig.ServerName = "example.go.dev"
+
+	serverConfig := testConfig.Clone()
+	serverConfig.MinVersion = VersionTLS13
+
+	cli := newTestQUICClient(t, clientConfig)
+	cli.conn.SetTransportParameters(nil)
+	srv := newTestQUICServer(t, serverConfig)
+	srv.conn.SetTransportParameters(nil)
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != nil {
+		t.Fatalf("error during first connection handshake: %v", err)
+	}
+	if cli.conn.ConnectionState().DidResume {
+		t.Errorf("first connection unexpectedly used session resumption")
+	}
+
+	cli2 := newTestQUICClient(t, clientConfig)
+	cli2.conn.SetTransportParameters(nil)
+	srv2 := newTestQUICServer(t, serverConfig)
+	srv2.conn.SetTransportParameters(nil)
+	if err := runTestQUICConnection(context.Background(), cli2, srv2, nil); err != nil {
+		t.Fatalf("error during second connection handshake: %v", err)
+	}
+	if !cli2.conn.ConnectionState().DidResume {
+		t.Errorf("second connection did not use session resumption")
+	}
+}
+
+func TestQUICPostHandshakeClientAuthentication(t *testing.T) {
+	// RFC 9001, Section 4.4.
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+	cli := newTestQUICClient(t, config)
+	cli.conn.SetTransportParameters(nil)
+	srv := newTestQUICServer(t, config)
+	srv.conn.SetTransportParameters(nil)
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != nil {
+		t.Fatalf("error during connection handshake: %v", err)
+	}
+
+	certReq := new(certificateRequestMsgTLS13)
+	certReq.ocspStapling = true
+	certReq.scts = true
+	certReq.supportedSignatureAlgorithms = supportedSignatureAlgorithms()
+	certReqBytes, err := certReq.marshal()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := cli.conn.HandleData(QUICEncryptionLevelApplication, append([]byte{
+		byte(typeCertificateRequest),
+		byte(0), byte(0), byte(len(certReqBytes)),
+	}, certReqBytes...)); err == nil {
+		t.Fatalf("post-handshake authentication request: got no error, want one")
+	}
+}
+
+func TestQUICPostHandshakeKeyUpdate(t *testing.T) {
+	// RFC 9001, Section 6.
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+	cli := newTestQUICClient(t, config)
+	cli.conn.SetTransportParameters(nil)
+	srv := newTestQUICServer(t, config)
+	srv.conn.SetTransportParameters(nil)
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != nil {
+		t.Fatalf("error during connection handshake: %v", err)
+	}
+
+	keyUpdate := new(keyUpdateMsg)
+	keyUpdateBytes, err := keyUpdate.marshal()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := cli.conn.HandleData(QUICEncryptionLevelApplication, append([]byte{
+		byte(typeKeyUpdate),
+		byte(0), byte(0), byte(len(keyUpdateBytes)),
+	}, keyUpdateBytes...)); !errors.Is(err, alertUnexpectedMessage) {
+		t.Fatalf("key update request: got error %v, want alertUnexpectedMessage", err)
+	}
+}
+
+func TestQUICHandshakeError(t *testing.T) {
+	clientConfig := testConfig.Clone()
+	clientConfig.MinVersion = VersionTLS13
+	clientConfig.InsecureSkipVerify = false
+	clientConfig.ServerName = "name"
+
+	serverConfig := testConfig.Clone()
+	serverConfig.MinVersion = VersionTLS13
+
+	cli := newTestQUICClient(t, clientConfig)
+	cli.conn.SetTransportParameters(nil)
+	srv := newTestQUICServer(t, serverConfig)
+	srv.conn.SetTransportParameters(nil)
+	err := runTestQUICConnection(context.Background(), cli, srv, nil)
+	if !errors.Is(err, AlertError(alertBadCertificate)) {
+		t.Errorf("connection handshake terminated with error %q, want alertBadCertificate", err)
+	}
+	var e *CertificateVerificationError
+	if !errors.As(err, &e) {
+		t.Errorf("connection handshake terminated with error %q, want CertificateVerificationError", err)
+	}
+}
+
+// Test that QUICConn.ConnectionState can be used during the handshake,
+// and that it reports the application protocol as soon as it has been
+// negotiated.
+func TestQUICConnectionState(t *testing.T) {
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+	config.NextProtos = []string{"h3"}
+	cli := newTestQUICClient(t, config)
+	cli.conn.SetTransportParameters(nil)
+	srv := newTestQUICServer(t, config)
+	srv.conn.SetTransportParameters(nil)
+	onHandleCryptoData := func() {
+		cliCS := cli.conn.ConnectionState()
+		cliWantALPN := ""
+		if _, ok := cli.readSecret[QUICEncryptionLevelApplication]; ok {
+			cliWantALPN = "h3"
+		}
+		if want, got := cliCS.NegotiatedProtocol, cliWantALPN; want != got {
+			t.Errorf("cli.ConnectionState().NegotiatedProtocol = %q, want %q", want, got)
+		}
+
+		srvCS := srv.conn.ConnectionState()
+		srvWantALPN := ""
+		if _, ok := srv.readSecret[QUICEncryptionLevelHandshake]; ok {
+			srvWantALPN = "h3"
+		}
+		if want, got := srvCS.NegotiatedProtocol, srvWantALPN; want != got {
+			t.Errorf("srv.ConnectionState().NegotiatedProtocol = %q, want %q", want, got)
+		}
+	}
+	if err := runTestQUICConnection(context.Background(), cli, srv, onHandleCryptoData); err != nil {
+		t.Fatalf("error during connection handshake: %v", err)
+	}
+}
+
+func TestQUICStartContextPropagation(t *testing.T) {
+	const key = "key"
+	const value = "value"
+	ctx := context.WithValue(context.Background(), key, value)
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+	calls := 0
+	config.GetConfigForClient = func(info *ClientHelloInfo) (*Config, error) {
+		calls++
+		got, _ := info.Context().Value(key).(string)
+		if got != value {
+			t.Errorf("GetConfigForClient context key %q has value %q, want %q", key, got, value)
+		}
+		return nil, nil
+	}
+	cli := newTestQUICClient(t, config)
+	cli.conn.SetTransportParameters(nil)
+	srv := newTestQUICServer(t, config)
+	srv.conn.SetTransportParameters(nil)
+	if err := runTestQUICConnection(ctx, cli, srv, nil); err != nil {
+		t.Fatalf("error during connection handshake: %v", err)
+	}
+	if calls != 1 {
+		t.Errorf("GetConfigForClient called %v times, want 1", calls)
+	}
+}
+
+func TestQUICDelayedTransportParameters(t *testing.T) {
+	clientConfig := testConfig.Clone()
+	clientConfig.MinVersion = VersionTLS13
+	clientConfig.ClientSessionCache = NewLRUClientSessionCache(1)
+	clientConfig.ServerName = "example.go.dev"
+
+	serverConfig := testConfig.Clone()
+	serverConfig.MinVersion = VersionTLS13
+
+	cliParams := "client params"
+	srvParams := "server params"
+
+	cli := newTestQUICClient(t, clientConfig)
+	srv := newTestQUICServer(t, serverConfig)
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != errTransportParametersRequired {
+		t.Fatalf("handshake with no client parameters: %v; want errTransportParametersRequired", err)
+	}
+	cli.conn.SetTransportParameters([]byte(cliParams))
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != errTransportParametersRequired {
+		t.Fatalf("handshake with no server parameters: %v; want errTransportParametersRequired", err)
+	}
+	srv.conn.SetTransportParameters([]byte(srvParams))
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != nil {
+		t.Fatalf("error during connection handshake: %v", err)
+	}
+
+	if got, want := string(cli.gotParams), srvParams; got != want {
+		t.Errorf("client got transport params: %q, want %q", got, want)
+	}
+	if got, want := string(srv.gotParams), cliParams; got != want {
+		t.Errorf("server got transport params: %q, want %q", got, want)
+	}
+}
+
+func TestQUICEmptyTransportParameters(t *testing.T) {
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+
+	cli := newTestQUICClient(t, config)
+	cli.conn.SetTransportParameters(nil)
+	srv := newTestQUICServer(t, config)
+	srv.conn.SetTransportParameters(nil)
+	if err := runTestQUICConnection(context.Background(), cli, srv, nil); err != nil {
+		t.Fatalf("error during connection handshake: %v", err)
+	}
+
+	if cli.gotParams == nil {
+		t.Errorf("client did not get transport params")
+	}
+	if srv.gotParams == nil {
+		t.Errorf("server did not get transport params")
+	}
+	if len(cli.gotParams) != 0 {
+		t.Errorf("client got transport params: %v, want empty", cli.gotParams)
+	}
+	if len(srv.gotParams) != 0 {
+		t.Errorf("server got transport params: %v, want empty", srv.gotParams)
+	}
+}
+
+func TestQUICCanceledWaitingForData(t *testing.T) {
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+	cli := newTestQUICClient(t, config)
+	cli.conn.SetTransportParameters(nil)
+	cli.conn.Start(context.Background())
+	for cli.conn.NextEvent().Kind != QUICNoEvent {
+	}
+	err := cli.conn.Close()
+	if !errors.Is(err, alertCloseNotify) {
+		t.Errorf("conn.Close() = %v, want alertCloseNotify", err)
+	}
+}
+
+func TestQUICCanceledWaitingForTransportParams(t *testing.T) {
+	config := testConfig.Clone()
+	config.MinVersion = VersionTLS13
+	cli := newTestQUICClient(t, config)
+	cli.conn.Start(context.Background())
+	for cli.conn.NextEvent().Kind != QUICTransportParametersRequired {
+	}
+	err := cli.conn.Close()
+	if !errors.Is(err, alertCloseNotify) {
+		t.Errorf("conn.Close() = %v, want alertCloseNotify", err)
+	}
+}