diff --git a/metadata/metadata.go b/metadata/metadata.go
index 954c0f77..3c0ca7a3 100644
--- a/metadata/metadata.go
+++ b/metadata/metadata.go
@@ -117,10 +117,17 @@ func (md MD) Len() int {
 
 // Copy returns a copy of md.
 func (md MD) Copy() MD {
+	return Join(md)
+}
+
+// Join joins any number of MDs into a single MD.
+// The order of values for each key is determined by the order in which
+// the MDs containing those values are presented to Join.
+func Join(mds ...MD) MD {
 	out := MD{}
-	for k, v := range md {
-		for _, i := range v {
-			out[k] = append(out[k], i)
+	for _, md := range mds {
+		for k, v := range md {
+			out[k] = append(out[k], v...)
 		}
 	}
 	return out
diff --git a/metadata/metadata_test.go b/metadata/metadata_test.go
index 99e86820..fef0a0f8 100644
--- a/metadata/metadata_test.go
+++ b/metadata/metadata_test.go
@@ -107,3 +107,33 @@ func TestPairsMD(t *testing.T) {
 		}
 	}
 }
+
+func TestCopy(t *testing.T) {
+	const key, val = "key", "val"
+	orig := Pairs(key, val)
+	copy := orig.Copy()
+	if !reflect.DeepEqual(orig, copy) {
+		t.Errorf("copied value not equal to the original, got %v, want %v", copy, orig)
+	}
+	orig[key][0] = "foo"
+	if v := copy[key][0]; v != val {
+		t.Errorf("change in original should not affect copy, got %q, want %q", v, val)
+	}
+}
+
+func TestJoin(t *testing.T) {
+	for _, test := range []struct {
+		mds  []MD
+		want MD
+	}{
+		{[]MD{}, MD{}},
+		{[]MD{Pairs("foo", "bar")}, Pairs("foo", "bar")},
+		{[]MD{Pairs("foo", "bar"), Pairs("foo", "baz")}, Pairs("foo", "bar", "foo", "baz")},
+		{[]MD{Pairs("foo", "bar"), Pairs("foo", "baz"), Pairs("zip", "zap")}, Pairs("foo", "bar", "foo", "baz", "zip", "zap")},
+	} {
+		md := Join(test.mds...)
+		if !reflect.DeepEqual(md, test.want) {
+			t.Errorf("context's metadata is %v, want %v", md, test.want)
+		}
+	}
+}