diff --git a/client_ext_test.go b/client_ext_test.go
index e0ba6381..bfe4e399 100644
--- a/client_ext_test.go
+++ b/client_ext_test.go
@@ -97,7 +97,8 @@ func TestClientPeer(t *testing.T) {
 			_, closeErr := clientStream.CloseAndReceive()
 			assert.Nil(t, closeErr)
 		})
-		assert.NotNil(t, clientStream.Peer().Addr)
+		assert.NotZero(t, clientStream.Peer().Addr)
+		assert.NotZero(t, clientStream.Peer().Protocol)
 		err = clientStream.Send(&pingv1.SumRequest{})
 		assert.Nil(t, err)
 		// server streaming
@@ -112,7 +113,8 @@ func TestClientPeer(t *testing.T) {
 			assert.Nil(t, bidiStream.CloseRequest())
 			assert.Nil(t, bidiStream.CloseResponse())
 		})
-		assert.NotNil(t, bidiStream.Peer().Addr)
+		assert.NotZero(t, bidiStream.Peer().Addr)
+		assert.NotZero(t, bidiStream.Peer().Protocol)
 		err = bidiStream.Send(&pingv1.CumSumRequest{})
 		assert.Nil(t, err)
 	}
@@ -138,6 +140,7 @@ type assertPeerInterceptor struct {
 func (a *assertPeerInterceptor) WrapUnary(next connect.UnaryFunc) connect.UnaryFunc {
 	return func(ctx context.Context, req connect.AnyRequest) (connect.AnyResponse, error) {
 		assert.NotZero(a.tb, req.Peer().Addr)
+		assert.NotZero(a.tb, req.Peer().Protocol)
 		return next(ctx, req)
 	}
 }
@@ -146,6 +149,7 @@ func (a *assertPeerInterceptor) WrapStreamingClient(next connect.StreamingClient
 	return func(ctx context.Context, spec connect.Spec) connect.StreamingClientConn {
 		conn := next(ctx, spec)
 		assert.NotZero(a.tb, conn.Peer().Addr)
+		assert.NotZero(a.tb, conn.Peer().Protocol)
 		return conn
 	}
 }
@@ -153,6 +157,7 @@ func (a *assertPeerInterceptor) WrapStreamingClient(next connect.StreamingClient
 func (a *assertPeerInterceptor) WrapStreamingHandler(next connect.StreamingHandlerFunc) connect.StreamingHandlerFunc {
 	return func(ctx context.Context, conn connect.StreamingHandlerConn) error {
 		assert.NotZero(a.tb, conn.Peer().Addr)
+		assert.NotZero(a.tb, conn.Peer().Protocol)
 		return next(ctx, conn)
 	}
 }
diff --git a/connect.go b/connect.go
index 283ca9f7..d04408e8 100644
--- a/connect.go
+++ b/connect.go
@@ -253,19 +253,26 @@ type Spec struct {
 	IsClient   bool   // otherwise we're in a handler
 }
 
-// Peer describes the other party to an RPC. When accessed client-side, Addr
-// contains the host or host:port from the server's URL. When accessed
-// server-side, Addr contains the client's address in IP:port format.
+// Peer describes the other party to an RPC.
+//
+// When accessed client-side, Addr contains the host or host:port from the
+// server's URL. When accessed server-side, Addr contains the client's address
+// in IP:port format.
+//
+// On both the client and the server, Protocol is the RPC protocol in use.
+// Currently, it's either [ProtocolConnect], [ProtocolGRPC], or
+// [ProtocolGRPCWeb], but additional protocols may be added in the future.
 type Peer struct {
-	Addr string
+	Addr     string
+	Protocol string
 }
 
-func newPeerFromURL(s string) Peer {
-	u, err := url.Parse(s)
-	if err != nil {
-		return Peer{}
+func newPeerFromURL(urlString, protocol string) Peer {
+	peer := Peer{Protocol: protocol}
+	if u, err := url.Parse(urlString); err == nil {
+		peer.Addr = u.Host
 	}
-	return Peer{Addr: u.Host}
+	return peer
 }
 
 // handlerConnCloser extends HandlerConn with a method for handlers to
diff --git a/connect_ext_test.go b/connect_ext_test.go
index ff5313b4..5e7f7dc3 100644
--- a/connect_ext_test.go
+++ b/connect_ext_test.go
@@ -1497,6 +1497,9 @@ func (p pingServer) Ping(ctx context.Context, request *connect.Request[pingv1.Pi
 	if request.Peer().Addr == "" {
 		return nil, connect.NewError(connect.CodeInternal, errors.New("no peer address"))
 	}
+	if request.Peer().Protocol == "" {
+		return nil, connect.NewError(connect.CodeInternal, errors.New("no peer protocol"))
+	}
 	response := connect.NewResponse(
 		&pingv1.PingResponse{
 			Number: request.Msg.Number,
@@ -1515,6 +1518,9 @@ func (p pingServer) Fail(ctx context.Context, request *connect.Request[pingv1.Fa
 	if request.Peer().Addr == "" {
 		return nil, connect.NewError(connect.CodeInternal, errors.New("no peer address"))
 	}
+	if request.Peer().Protocol == "" {
+		return nil, connect.NewError(connect.CodeInternal, errors.New("no peer protocol"))
+	}
 	err := connect.NewError(connect.Code(request.Msg.Code), errors.New(errorMessage))
 	err.Meta().Set(handlerHeader, headerValue)
 	err.Meta().Set(handlerTrailer, trailerValue)
@@ -1533,6 +1539,9 @@ func (p pingServer) Sum(
 	if stream.Peer().Addr == "" {
 		return nil, connect.NewError(connect.CodeInternal, errors.New("no peer address"))
 	}
+	if stream.Peer().Protocol == "" {
+		return nil, connect.NewError(connect.CodeInternal, errors.New("no peer protocol"))
+	}
 	var sum int64
 	for stream.Receive() {
 		sum += stream.Msg().Number
@@ -1557,6 +1566,9 @@ func (p pingServer) CountUp(
 	if request.Peer().Addr == "" {
 		return connect.NewError(connect.CodeInternal, errors.New("no peer address"))
 	}
+	if request.Peer().Protocol == "" {
+		return connect.NewError(connect.CodeInternal, errors.New("no peer protocol"))
+	}
 	if request.Msg.Number <= 0 {
 		return connect.NewError(connect.CodeInvalidArgument, fmt.Errorf(
 			"number must be positive: got %v",
@@ -1586,6 +1598,9 @@ func (p pingServer) CumSum(
 	if stream.Peer().Addr == "" {
 		return connect.NewError(connect.CodeInternal, errors.New("no peer address"))
 	}
+	if stream.Peer().Protocol == "" {
+		return connect.NewError(connect.CodeInternal, errors.New("no peer address"))
+	}
 	stream.ResponseHeader().Set(handlerHeader, headerValue)
 	stream.ResponseTrailer().Set(handlerTrailer, trailerValue)
 	for {
diff --git a/protocol.go b/protocol.go
index 8f0e7060..0fe92387 100644
--- a/protocol.go
+++ b/protocol.go
@@ -26,6 +26,14 @@ import (
 	"strings"
 )
 
+// The names of the Connect, gRPC, and gRPC-Web protocols (as exposed by
+// [Peer.Protocol]). Additional protocols may be added in the future.
+const (
+	ProtocolConnect = "connect"
+	ProtocolGRPC    = "grpc"
+	ProtocolGRPCWeb = "grpcweb"
+)
+
 const (
 	headerContentType = "Content-Type"
 	headerUserAgent   = "User-Agent"
diff --git a/protocol_connect.go b/protocol_connect.go
index 069d4e35..13d32e23 100644
--- a/protocol_connect.go
+++ b/protocol_connect.go
@@ -151,7 +151,10 @@ func (h *connectHandler) NewConn(
 	codec := h.Codecs.Get(codecName) // handler.go guarantees this is not nil
 
 	var conn handlerConnCloser
-	peer := Peer{Addr: request.RemoteAddr}
+	peer := Peer{
+		Addr:     request.RemoteAddr,
+		Protocol: ProtocolConnect,
+	}
 	if h.Spec.StreamType == StreamTypeUnary {
 		conn = &connectUnaryHandlerConn{
 			spec:           h.Spec,
@@ -221,7 +224,7 @@ type connectClient struct {
 }
 
 func (c *connectClient) Peer() Peer {
-	return newPeerFromURL(c.URL)
+	return newPeerFromURL(c.URL, ProtocolConnect)
 }
 
 func (c *connectClient) WriteRequestHeader(streamType StreamType, header http.Header) {
diff --git a/protocol_grpc.go b/protocol_grpc.go
index bd2c14e1..36f957af 100644
--- a/protocol_grpc.go
+++ b/protocol_grpc.go
@@ -161,9 +161,16 @@ func (g *grpcHandler) NewConn(
 
 	codecName := grpcCodecFromContentType(g.web, request.Header.Get(headerContentType))
 	codec := g.Codecs.Get(codecName) // handler.go guarantees this is not nil
+	protocolName := ProtocolGRPC
+	if g.web {
+		protocolName = ProtocolGRPCWeb
+	}
 	conn := wrapHandlerConnWithCodedErrors(&grpcHandlerConn{
-		spec:       g.Spec,
-		peer:       Peer{Addr: request.RemoteAddr},
+		spec: g.Spec,
+		peer: Peer{
+			Addr:     request.RemoteAddr,
+			Protocol: protocolName,
+		},
 		web:        g.web,
 		bufferPool: g.BufferPool,
 		protobuf:   g.Codecs.Protobuf(), // for errors
@@ -207,7 +214,10 @@ type grpcClient struct {
 }
 
 func (g *grpcClient) Peer() Peer {
-	return newPeerFromURL(g.URL)
+	if g.web {
+		return newPeerFromURL(g.URL, ProtocolGRPCWeb)
+	}
+	return newPeerFromURL(g.URL, ProtocolGRPC)
 }
 
 func (g *grpcClient) WriteRequestHeader(_ StreamType, header http.Header) {