diff --git a/bigtable/admin.go b/bigtable/admin.go
index c5666e51e36c..d0f03664cdee 100644
--- a/bigtable/admin.go
+++ b/bigtable/admin.go
@@ -75,7 +75,7 @@ func (ac *AdminClient) instancePrefix() string {
 
 // Tables returns a list of the tables in the instance.
 func (ac *AdminClient) Tables(ctx context.Context) ([]string, error) {
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.ListTablesRequest{
 		Parent: prefix,
@@ -94,7 +94,7 @@ func (ac *AdminClient) Tables(ctx context.Context) ([]string, error) {
 // CreateTable creates a new table in the instance.
 // This method may return before the table's creation is complete.
 func (ac *AdminClient) CreateTable(ctx context.Context, table string) error {
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.CreateTableRequest{
 		Parent:  prefix,
@@ -114,7 +114,7 @@ func (ac *AdminClient) CreatePresplitTable(ctx context.Context, table string, sp
 	for _, split := range split_keys {
 		req_splits = append(req_splits, &btapb.CreateTableRequest_Split{[]byte(split)})
 	}
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.CreateTableRequest{
 		Parent:        prefix,
@@ -128,7 +128,7 @@ func (ac *AdminClient) CreatePresplitTable(ctx context.Context, table string, sp
 // CreateColumnFamily creates a new column family in a table.
 func (ac *AdminClient) CreateColumnFamily(ctx context.Context, table, family string) error {
 	// TODO(dsymonds): Permit specifying gcexpr and any other family settings.
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.ModifyColumnFamiliesRequest{
 		Name: prefix + "/tables/" + table,
@@ -143,7 +143,7 @@ func (ac *AdminClient) CreateColumnFamily(ctx context.Context, table, family str
 
 // DeleteTable deletes a table and all of its data.
 func (ac *AdminClient) DeleteTable(ctx context.Context, table string) error {
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.DeleteTableRequest{
 		Name: prefix + "/tables/" + table,
@@ -154,7 +154,7 @@ func (ac *AdminClient) DeleteTable(ctx context.Context, table string) error {
 
 // DeleteColumnFamily deletes a column family in a table and all of its data.
 func (ac *AdminClient) DeleteColumnFamily(ctx context.Context, table, family string) error {
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.ModifyColumnFamiliesRequest{
 		Name: prefix + "/tables/" + table,
@@ -174,7 +174,7 @@ type TableInfo struct {
 
 // TableInfo retrieves information about a table.
 func (ac *AdminClient) TableInfo(ctx context.Context, table string) (*TableInfo, error) {
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.GetTableRequest{
 		Name: prefix + "/tables/" + table,
@@ -194,7 +194,7 @@ func (ac *AdminClient) TableInfo(ctx context.Context, table string) (*TableInfo,
 // GC executes opportunistically in the background; table reads may return data
 // matching the GC policy.
 func (ac *AdminClient) SetGCPolicy(ctx context.Context, table, family string, policy GCPolicy) error {
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.ModifyColumnFamiliesRequest{
 		Name: prefix + "/tables/" + table,
@@ -209,7 +209,7 @@ func (ac *AdminClient) SetGCPolicy(ctx context.Context, table, family string, po
 
 // DropRowRange permanently deletes a row range from the specified table.
 func (ac *AdminClient) DropRowRange(ctx context.Context, table, rowKeyPrefix string) error {
-	ctx = mergeMetadata(ctx, ac.md)
+	ctx = mergeOutgoingMetadata(ctx, ac.md)
 	prefix := ac.instancePrefix()
 	req := &btapb.DropRowRangeRequest{
 		Name:   prefix + "/tables/" + table,
@@ -291,7 +291,7 @@ var instanceNameRegexp = regexp.MustCompile(`^projects/([^/]+)/instances/([a-z][
 // CreateInstance creates a new instance in the project.
 // This method will return when the instance has been created or when an error occurs.
 func (iac *InstanceAdminClient) CreateInstance(ctx context.Context, conf *InstanceConf) error {
-	ctx = mergeMetadata(ctx, iac.md)
+	ctx = mergeOutgoingMetadata(ctx, iac.md)
 	req := &btapb.CreateInstanceRequest{
 		Parent:     "projects/" + iac.project,
 		InstanceId: conf.InstanceId,
@@ -315,7 +315,7 @@ func (iac *InstanceAdminClient) CreateInstance(ctx context.Context, conf *Instan
 
 // DeleteInstance deletes an instance from the project.
 func (iac *InstanceAdminClient) DeleteInstance(ctx context.Context, instanceId string) error {
-	ctx = mergeMetadata(ctx, iac.md)
+	ctx = mergeOutgoingMetadata(ctx, iac.md)
 	req := &btapb.DeleteInstanceRequest{"projects/" + iac.project + "/instances/" + instanceId}
 	_, err := iac.iClient.DeleteInstance(ctx, req)
 	return err
@@ -323,7 +323,7 @@ func (iac *InstanceAdminClient) DeleteInstance(ctx context.Context, instanceId s
 
 // Instances returns a list of instances in the project.
 func (iac *InstanceAdminClient) Instances(ctx context.Context) ([]*InstanceInfo, error) {
-	ctx = mergeMetadata(ctx, iac.md)
+	ctx = mergeOutgoingMetadata(ctx, iac.md)
 	req := &btapb.ListInstancesRequest{
 		Parent: "projects/" + iac.project,
 	}
diff --git a/bigtable/bigtable.go b/bigtable/bigtable.go
index 374ed573273f..5c2129cb7723 100644
--- a/bigtable/bigtable.go
+++ b/bigtable/bigtable.go
@@ -73,7 +73,7 @@ func (c *Client) Close() error {
 }
 
 var (
-	idempotentRetryCodes  = []codes.Code{codes.DeadlineExceeded, codes.Unavailable, codes.Aborted,codes.Internal}
+	idempotentRetryCodes  = []codes.Code{codes.DeadlineExceeded, codes.Unavailable, codes.Aborted, codes.Internal}
 	isIdempotentRetryCode = make(map[codes.Code]bool)
 	retryOptions          = []gax.CallOption{
 		gax.WithDelayTimeoutSettings(100*time.Millisecond, 2000*time.Millisecond, 1.2),
@@ -120,7 +120,7 @@ func (c *Client) Open(table string) *Table {
 // By default, the yielded rows will contain all values in all cells.
 // Use RowFilter to limit the cells returned.
 func (t *Table) ReadRows(ctx context.Context, arg RowSet, f func(Row) bool, opts ...ReadOption) error {
-	ctx = mergeMetadata(ctx, t.md)
+	ctx = mergeOutgoingMetadata(ctx, t.md)
 
 	var prevRowKey string
 	err := gax.Invoke(ctx, func(ctx context.Context) error {
@@ -337,7 +337,7 @@ func (r RowRangeList) retainRowsAfter(lastRowKey string) RowSet {
 }
 
 func (r RowRangeList) valid() bool {
- 	for _, rr := range r {
+	for _, rr := range r {
 		if rr.valid() {
 			return true
 		}
@@ -420,7 +420,7 @@ func mutationsAreRetryable(muts []*btpb.Mutation) bool {
 
 // Apply applies a Mutation to a specific row.
 func (t *Table) Apply(ctx context.Context, row string, m *Mutation, opts ...ApplyOption) error {
-	ctx = mergeMetadata(ctx, t.md)
+	ctx = mergeOutgoingMetadata(ctx, t.md)
 	after := func(res proto.Message) {
 		for _, o := range opts {
 			o.after(res)
@@ -582,7 +582,7 @@ type entryErr struct {
 //
 // Conditional mutations cannot be applied in bulk and providing one will result in an error.
 func (t *Table) ApplyBulk(ctx context.Context, rowKeys []string, muts []*Mutation, opts ...ApplyOption) ([]error, error) {
-	ctx = mergeMetadata(ctx, t.md)
+	ctx = mergeOutgoingMetadata(ctx, t.md)
 	if len(rowKeys) != len(muts) {
 		return nil, fmt.Errorf("mismatched rowKeys and mutation array lengths: %d, %d", len(rowKeys), len(muts))
 	}
@@ -711,13 +711,13 @@ func (ts Timestamp) TruncateToMilliseconds() Timestamp {
 	if ts == ServerTime {
 		return ts
 	}
-	return ts - ts % 1000
+	return ts - ts%1000
 }
 
 // ApplyReadModifyWrite applies a ReadModifyWrite to a specific row.
 // It returns the newly written cells.
 func (t *Table) ApplyReadModifyWrite(ctx context.Context, row string, m *ReadModifyWrite) (Row, error) {
-	ctx = mergeMetadata(ctx, t.md)
+	ctx = mergeOutgoingMetadata(ctx, t.md)
 	req := &btpb.ReadModifyWriteRowRequest{
 		TableName: t.c.fullTableName(t.table),
 		RowKey:    []byte(row),
@@ -774,9 +774,9 @@ func (m *ReadModifyWrite) Increment(family, column string, delta int64) {
 	})
 }
 
-// mergeMetadata returns a context populated by the existing metadata, if any,
-// joined with internal metadata.
-func mergeMetadata(ctx context.Context, md metadata.MD) context.Context {
-	mdCopy, _ := metadata.FromContext(ctx)
-	return metadata.NewContext(ctx, metadata.Join(mdCopy, md))
+// mergeOutgoingMetadata returns a context populated by the existing outgoing metadata,
+// if any, joined with internal metadata.
+func mergeOutgoingMetadata(ctx context.Context, md metadata.MD) context.Context {
+	mdCopy, _ := metadata.FromOutgoingContext(ctx)
+	return metadata.NewOutgoingContext(ctx, metadata.Join(mdCopy, md))
 }
diff --git a/datastore/datastore.go b/datastore/datastore.go
index 91f92c437b51..e9ffbfab7f7c 100644
--- a/datastore/datastore.go
+++ b/datastore/datastore.go
@@ -71,27 +71,27 @@ func newDatastoreClient(conn *grpc.ClientConn, projectID string) pb.DatastoreCli
 }
 
 func (dc *datastoreClient) Lookup(ctx context.Context, in *pb.LookupRequest, opts ...grpc.CallOption) (*pb.LookupResponse, error) {
-	return dc.c.Lookup(metadata.NewContext(ctx, dc.md), in, opts...)
+	return dc.c.Lookup(metadata.NewOutgoingContext(ctx, dc.md), in, opts...)
 }
 
 func (dc *datastoreClient) RunQuery(ctx context.Context, in *pb.RunQueryRequest, opts ...grpc.CallOption) (*pb.RunQueryResponse, error) {
-	return dc.c.RunQuery(metadata.NewContext(ctx, dc.md), in, opts...)
+	return dc.c.RunQuery(metadata.NewOutgoingContext(ctx, dc.md), in, opts...)
 }
 
 func (dc *datastoreClient) BeginTransaction(ctx context.Context, in *pb.BeginTransactionRequest, opts ...grpc.CallOption) (*pb.BeginTransactionResponse, error) {
-	return dc.c.BeginTransaction(metadata.NewContext(ctx, dc.md), in, opts...)
+	return dc.c.BeginTransaction(metadata.NewOutgoingContext(ctx, dc.md), in, opts...)
 }
 
 func (dc *datastoreClient) Commit(ctx context.Context, in *pb.CommitRequest, opts ...grpc.CallOption) (*pb.CommitResponse, error) {
-	return dc.c.Commit(metadata.NewContext(ctx, dc.md), in, opts...)
+	return dc.c.Commit(metadata.NewOutgoingContext(ctx, dc.md), in, opts...)
 }
 
 func (dc *datastoreClient) Rollback(ctx context.Context, in *pb.RollbackRequest, opts ...grpc.CallOption) (*pb.RollbackResponse, error) {
-	return dc.c.Rollback(metadata.NewContext(ctx, dc.md), in, opts...)
+	return dc.c.Rollback(metadata.NewOutgoingContext(ctx, dc.md), in, opts...)
 }
 
 func (dc *datastoreClient) AllocateIds(ctx context.Context, in *pb.AllocateIdsRequest, opts ...grpc.CallOption) (*pb.AllocateIdsResponse, error) {
-	return dc.c.AllocateIds(metadata.NewContext(ctx, dc.md), in, opts...)
+	return dc.c.AllocateIds(metadata.NewOutgoingContext(ctx, dc.md), in, opts...)
 }
 
 // Client is a client for reading and writing data in a datastore dataset.
diff --git a/spanner/client.go b/spanner/client.go
index 92e7381b6ac6..3c979e740a85 100644
--- a/spanner/client.go
+++ b/spanner/client.go
@@ -96,12 +96,12 @@ func errDial(ci int, err error) error {
 	return e
 }
 
-func contextWithMetadata(ctx context.Context, md metadata.MD) context.Context {
-	existing, ok := metadata.FromContext(ctx)
+func contextWithOutgoingMetadata(ctx context.Context, md metadata.MD) context.Context {
+	existing, ok := metadata.FromOutgoingContext(ctx)
 	if ok {
 		md = metadata.Join(existing, md)
 	}
-	return metadata.NewContext(ctx, md)
+	return metadata.NewOutgoingContext(ctx, md)
 }
 
 // NewClient creates a client to a database. A valid database name has the
diff --git a/spanner/session.go b/spanner/session.go
index 58eb96d317d2..95c88782d45e 100644
--- a/spanner/session.go
+++ b/spanner/session.go
@@ -166,7 +166,7 @@ func (s *session) ping() error {
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
 	defer cancel()
 	return runRetryable(ctx, func(ctx context.Context) error {
-		_, err := s.client.GetSession(contextWithMetadata(ctx, s.pool.md), &sppb.GetSessionRequest{Name: s.getID()}) // s.getID is safe even when s is invalid.
+		_, err := s.client.GetSession(contextWithOutgoingMetadata(ctx, s.pool.md), &sppb.GetSessionRequest{Name: s.getID()}) // s.getID is safe even when s is invalid.
 		return err
 	})
 }
@@ -185,7 +185,7 @@ func (s *session) refreshIdle() bool {
 	defer cancel()
 	var sid string
 	err := runRetryable(ctx, func(ctx context.Context) error {
-		session, e := s.client.CreateSession(contextWithMetadata(ctx, s.pool.md), &sppb.CreateSessionRequest{Database: s.pool.db})
+		session, e := s.client.CreateSession(contextWithOutgoingMetadata(ctx, s.pool.md), &sppb.CreateSessionRequest{Database: s.pool.db})
 		if e != nil {
 			return e
 		}
@@ -216,7 +216,7 @@ func (s *session) refreshIdle() bool {
 	// If we fail to explicitly destroy the session, it will be eventually garbage collected by
 	// Cloud Spanner.
 	if err = runRetryable(ctx, func(ctx context.Context) error {
-		_, e := s.client.DeleteSession(contextWithMetadata(ctx, s.pool.md), &sppb.DeleteSessionRequest{Name: sid})
+		_, e := s.client.DeleteSession(contextWithOutgoingMetadata(ctx, s.pool.md), &sppb.DeleteSessionRequest{Name: sid})
 		return e
 	}); err != nil {
 		return false
@@ -541,7 +541,7 @@ func (p *sessionPool) isHealthy(s *session) bool {
 // take returns a cached session if there are available ones; if there isn't any, it tries to allocate a new one.
 // Session returned by take should be used for read operations.
 func (p *sessionPool) take(ctx context.Context) (*sessionHandle, error) {
-	ctx = contextWithMetadata(ctx, p.md)
+	ctx = contextWithOutgoingMetadata(ctx, p.md)
 	for {
 		var (
 			s   *session
@@ -595,7 +595,7 @@ func (p *sessionPool) take(ctx context.Context) (*sessionHandle, error) {
 // takeWriteSession returns a write prepared cached session if there are available ones; if there isn't any, it tries to allocate a new one.
 // Session returned should be used for read write transactions.
 func (p *sessionPool) takeWriteSession(ctx context.Context) (*sessionHandle, error) {
-	ctx = contextWithMetadata(ctx, p.md)
+	ctx = contextWithOutgoingMetadata(ctx, p.md)
 	for {
 		var (
 			s   *session
@@ -927,7 +927,7 @@ func (hc *healthChecker) worker(i int) {
 		if ws != nil {
 			ctx, cancel := context.WithTimeout(context.Background(), time.Second)
 			defer cancel()
-			ws.prepareForWrite(contextWithMetadata(ctx, hc.pool.md))
+			ws.prepareForWrite(contextWithOutgoingMetadata(ctx, hc.pool.md))
 			hc.pool.recycle(ws)
 			hc.pool.mu.Lock()
 			hc.pool.prepareReqs--
diff --git a/spanner/transaction.go b/spanner/transaction.go
index 275cadef53a0..49977e9d2d79 100644
--- a/spanner/transaction.go
+++ b/spanner/transaction.go
@@ -84,7 +84,7 @@ func (t *txReadOnly) ReadUsingIndex(ctx context.Context, table, index string, ke
 		return &RowIterator{err: errSessionClosed(sh)}
 	}
 	return stream(
-		contextWithMetadata(ctx, sh.getMetadata()),
+		contextWithOutgoingMetadata(ctx, sh.getMetadata()),
 		func(ctx context.Context, resumeToken []byte) (streamingReceiver, error) {
 			return client.StreamingRead(ctx,
 				&sppb.ReadRequest{
@@ -150,7 +150,7 @@ func (t *txReadOnly) Query(ctx context.Context, statement Statement) *RowIterato
 		return &RowIterator{err: err}
 	}
 	return stream(
-		contextWithMetadata(ctx, sh.getMetadata()),
+		contextWithOutgoingMetadata(ctx, sh.getMetadata()),
 		func(ctx context.Context, resumeToken []byte) (streamingReceiver, error) {
 			req.ResumeToken = resumeToken
 			return client.ExecuteStreamingSql(ctx, req)
@@ -279,7 +279,7 @@ func (t *ReadOnlyTransaction) begin(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	err = runRetryable(contextWithMetadata(ctx, sh.getMetadata()), func(ctx context.Context) error {
+	err = runRetryable(contextWithOutgoingMetadata(ctx, sh.getMetadata()), func(ctx context.Context) error {
 		res, e := sh.getClient().BeginTransaction(ctx, &sppb.BeginTransactionRequest{
 			Session: sh.getID(),
 			Options: &sppb.TransactionOptions{
@@ -629,7 +629,7 @@ func (t *ReadWriteTransaction) begin(ctx context.Context) error {
 		t.state = txActive
 		return nil
 	}
-	tx, err := beginTransaction(contextWithMetadata(ctx, t.sh.getMetadata()), t.sh.getID(), t.sh.getClient())
+	tx, err := beginTransaction(contextWithOutgoingMetadata(ctx, t.sh.getMetadata()), t.sh.getID(), t.sh.getClient())
 	if err == nil {
 		t.tx = tx
 		t.state = txActive
@@ -656,7 +656,7 @@ func (t *ReadWriteTransaction) commit(ctx context.Context) (time.Time, error) {
 	if sid == "" || client == nil {
 		return ts, errSessionClosed(t.sh)
 	}
-	err = runRetryable(contextWithMetadata(ctx, t.sh.getMetadata()), func(ctx context.Context) error {
+	err = runRetryable(contextWithOutgoingMetadata(ctx, t.sh.getMetadata()), func(ctx context.Context) error {
 		var trailer metadata.MD
 		res, e := client.Commit(ctx, &sppb.CommitRequest{
 			Session: sid,
@@ -690,7 +690,7 @@ func (t *ReadWriteTransaction) rollback(ctx context.Context) {
 	if sid == "" || client == nil {
 		return
 	}
-	err := runRetryable(contextWithMetadata(ctx, t.sh.getMetadata()), func(ctx context.Context) error {
+	err := runRetryable(contextWithOutgoingMetadata(ctx, t.sh.getMetadata()), func(ctx context.Context) error {
 		_, e := client.Rollback(ctx, &sppb.RollbackRequest{
 			Session:       sid,
 			TransactionId: t.tx,
@@ -759,7 +759,7 @@ func (t *writeOnlyTransaction) applyAtLeastOnce(ctx context.Context, ms ...*Muta
 				return e
 			}
 		}
-		res, e := sh.getClient().Commit(contextWithMetadata(ctx, sh.getMetadata()), &sppb.CommitRequest{
+		res, e := sh.getClient().Commit(contextWithOutgoingMetadata(ctx, sh.getMetadata()), &sppb.CommitRequest{
 			Session: sh.getID(),
 			Transaction: &sppb.CommitRequest_SingleUseTransaction{
 				SingleUseTransaction: &sppb.TransactionOptions{
diff --git a/trace/grpc.go b/trace/grpc.go
index a55aa66d14ee..16ecf5f96f60 100644
--- a/trace/grpc.go
+++ b/trace/grpc.go
@@ -49,7 +49,7 @@ func grpcUnaryInterceptor(ctx context.Context, method string, req, reply interfa
 			md = md.Copy() // metadata is immutable, copy.
 			md[grpcMetadataKey] = []string{header}
 		}
-		ctx = metadata.NewContext(ctx, md)
+		ctx = metadata.NewOutgoingContext(ctx, md)
 	}
 
 	err := invoker(ctx, method, req, reply, cc, opts...)