diff --git a/metadata/context.go b/metadata/context.go
index 475e1b49..471b144a 100644
--- a/metadata/context.go
+++ b/metadata/context.go
@@ -1,3 +1,5 @@
+//go:build !exclude
+
 // Package metadata is a way of defining message headers
 package metadata
 
diff --git a/metadata/metadata.go b/metadata/metadata.go
index 347c4ec5..f2729e73 100644
--- a/metadata/metadata.go
+++ b/metadata/metadata.go
@@ -1,3 +1,5 @@
+//go:build !exclude
+
 // Package metadata is a way of defining message headers
 package metadata
 
diff --git a/metadata/metadata_grpc.go b/metadata/metadata_grpc.go
index 4c5102d3..f5f2bbf1 100644
--- a/metadata/metadata_grpc.go
+++ b/metadata/metadata_grpc.go
@@ -1,7 +1,7 @@
 //go:build exclude
 
-// TODO need compare with micro metadata
-package metadata
+// Package metadata TODO need compare with micro metadata
+package metadata // import "google.golang.org/grpc/metadata"
 
 import (
 	"context"
@@ -9,16 +9,11 @@ import (
 	"strings"
 )
 
-// DecodeKeyValue returns k, v, nil.
-//
-// Deprecated: use k and v directly instead.
-func DecodeKeyValue(k, v string) (string, string, error) {
-	return k, v, nil
-}
-
 // MD is a mapping from metadata keys to values. Users should use the following
 // two convenience functions New and Pairs to generate MD.
-type MD map[string]string
+type MD map[string][]string
+
+type Metadata map[string]string
 
 // New creates an MD from a given key-value map.
 //
@@ -36,7 +31,7 @@ func New(m map[string]string) MD {
 	md := make(MD, len(m))
 	for k, val := range m {
 		key := strings.ToLower(k)
-		md[key] = val
+		md[key] = append(md[key], val)
 	}
 	return md
 }
@@ -61,7 +56,7 @@ func Pairs(kv ...string) MD {
 	md := make(MD, len(kv)/2)
 	for i := 0; i < len(kv); i += 2 {
 		key := strings.ToLower(kv[i])
-		md[key] = kv[i+1]
+		md[key] = append(md[key], kv[i+1])
 	}
 	return md
 }
@@ -75,7 +70,7 @@ func (md MD) Len() int {
 func (md MD) Copy() MD {
 	out := make(MD, len(md))
 	for k, v := range md {
-		out[k] = v
+		out[k] = copyOf(v)
 	}
 	return out
 }
@@ -83,7 +78,7 @@ func (md MD) Copy() MD {
 // Get obtains the values for a given key.
 //
 // k is converted to lowercase before searching in md.
-func (md MD) Get(k string) string {
+func (md MD) Get(k string) []string {
 	k = strings.ToLower(k)
 	return md[k]
 }
@@ -91,7 +86,7 @@ func (md MD) Get(k string) string {
 // Set sets the value of a given key with a slice of values.
 //
 // k is converted to lowercase before storing in md.
-func (md MD) Set(k string, vals string) {
+func (md MD) Set(k string, vals ...string) {
 	if len(vals) == 0 {
 		return
 	}
@@ -103,12 +98,12 @@ func (md MD) Set(k string, vals string) {
 // that key.
 //
 // k is converted to lowercase before storing in md.
-func (md MD) Append(k string, vals string) {
+func (md MD) Append(k string, vals ...string) {
 	if len(vals) == 0 {
 		return
 	}
 	k = strings.ToLower(k)
-	md[k] = vals
+	md[k] = append(md[k], vals...)
 }
 
 // Delete removes the values for a given key k which is converted to lowercase
@@ -126,7 +121,7 @@ func Join(mds ...MD) MD {
 	out := MD{}
 	for _, md := range mds {
 		for k, v := range md {
-			out[k] = v
+			out[k] = append(out[k], v...)
 		}
 	}
 	return out
@@ -137,16 +132,26 @@ type mdOutgoingKey struct{}
 
 // NewIncomingContext creates a new context with incoming md attached. md must
 // not be modified after calling this function.
-func NewIncomingContext(ctx context.Context, md MD) context.Context {
-	return context.WithValue(ctx, mdIncomingKey{}, md)
+func NewIncomingContext(ctx context.Context, md Metadata) context.Context {
+	in := make(MD, len(md))
+	for k, v := range md {
+		in[k] = []string{v}
+	}
+
+	return context.WithValue(ctx, mdIncomingKey{}, in)
 }
 
 // NewOutgoingContext creates a new context with outgoing md attached. If used
 // in conjunction with AppendToOutgoingContext, NewOutgoingContext will
 // overwrite any previously-appended metadata. md must not be modified after
 // calling this function.
-func NewOutgoingContext(ctx context.Context, md MD) context.Context {
-	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md})
+func NewOutgoingContext(ctx context.Context, md Metadata) context.Context {
+	out := make(MD, len(md))
+	for k, v := range md {
+		out[k] = []string{v}
+	}
+
+	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: out})
 }
 
 // AppendToOutgoingContext returns a new context with the provided kv merged
@@ -157,70 +162,121 @@ func AppendToOutgoingContext(ctx context.Context, kv ...string) context.Context
 		panic(fmt.Sprintf("metadata: AppendToOutgoingContext got an odd number of input pairs for metadata: %d", len(kv)))
 	}
 	md, _ := ctx.Value(mdOutgoingKey{}).(rawMD)
-
+	added := make([][]string, len(md.added)+1)
+	copy(added, md.added)
 	kvCopy := make([]string, 0, len(kv))
 	for i := 0; i < len(kv); i += 2 {
 		kvCopy = append(kvCopy, strings.ToLower(kv[i]), kv[i+1])
 	}
-
-	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md.md})
+	added[len(added)-1] = kvCopy
+	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md.md, added: added})
 }
 
 // FromIncomingContext returns the incoming metadata in ctx if it exists.
 //
 // All keys in the returned MD are lowercase.
-func FromIncomingContext(ctx context.Context) (MD, bool) {
+func FromIncomingContext(ctx context.Context) (Metadata, bool) {
 	md, ok := ctx.Value(mdIncomingKey{}).(MD)
 	if !ok {
 		return nil, false
 	}
-	out := make(MD, len(md))
+	out := make(Metadata, len(md))
 	for k, v := range md {
 		// We need to manually convert all keys to lower case, because MD is a
 		// map, and there's no guarantee that the MD attached to the context is
 		// created using our helper functions.
-		key := strings.ToLower(k)
-		out[key] = v
+
+		if len(v) > 0 {
+			key := strings.ToLower(k)
+			out[key] = v[0]
+		}
+
 	}
 	return out, true
 }
 
+// ValueFromIncomingContext returns the metadata value corresponding to the metadata
+// key from the incoming metadata if it exists. Keys are matched in a case insensitive
+// manner.
+func ValueFromIncomingContext(ctx context.Context, key string) []string {
+	md, ok := ctx.Value(mdIncomingKey{}).(MD)
+	if !ok {
+		return nil
+	}
+
+	if v, ok := md[key]; ok {
+		return copyOf(v)
+	}
+	for k, v := range md {
+		// Case insensitive comparison: MD is a map, and there's no guarantee
+		// that the MD attached to the context is created using our helper
+		// functions.
+		if strings.EqualFold(k, key) {
+			return copyOf(v)
+		}
+	}
+	return nil
+}
+
+func copyOf(v []string) []string {
+	vals := make([]string, len(v))
+	copy(vals, v)
+	return vals
+}
+
 // fromOutgoingContextRaw returns the un-merged, intermediary contents of rawMD.
 //
 // Remember to perform strings.ToLower on the keys, for both the returned MD (MD
 // is a map, there's no guarantee it's created using our helper functions) and
 // the extra kv pairs (AppendToOutgoingContext doesn't turn them into
 // lowercase).
-func fromOutgoingContextRaw(ctx context.Context) (MD, bool) {
+func fromOutgoingContextRaw(ctx context.Context) (MD, [][]string, bool) {
 	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
 	if !ok {
-		return nil, false
+		return nil, nil, false
 	}
 
-	return raw.md, true
+	return raw.md, raw.added, true
 }
 
 // FromOutgoingContext returns the outgoing metadata in ctx if it exists.
 //
 // All keys in the returned MD are lowercase.
-func FromOutgoingContext(ctx context.Context) (MD, bool) {
+func FromOutgoingContext(ctx context.Context) (Metadata, bool) {
 	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
 	if !ok {
 		return nil, false
 	}
 
-	out := make(MD, len(raw.md))
+	mdSize := len(raw.md)
+	for i := range raw.added {
+		mdSize += len(raw.added[i]) / 2
+	}
+
+	out := make(Metadata, mdSize)
 	for k, v := range raw.md {
 		// We need to manually convert all keys to lower case, because MD is a
 		// map, and there's no guarantee that the MD attached to the context is
 		// created using our helper functions.
-		key := strings.ToLower(k)
-		out[key] = v
+		if len(v) > 0 {
+			key := strings.ToLower(k)
+			out[key] = v[0]
+		}
 	}
+	for _, added := range raw.added {
+		if len(added)%2 == 1 {
+			panic(fmt.Sprintf("metadata: FromOutgoingContext got an odd number of input pairs for metadata: %d", len(added)))
+		}
 
+		for i := 0; i < len(added); i += 2 {
+			key := strings.ToLower(added[i])
+			out[key] = added[i+1]
+		}
+	}
 	return out, ok
 }
 
 type rawMD struct {
-	md MD
+	md    MD
+	added [][]string
 }