diff --git a/api/api_proto/users.proto b/api/api_proto/users.proto
new file mode 100644
index 0000000..574dccd
--- /dev/null
+++ b/api/api_proto/users.proto
@@ -0,0 +1,193 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+syntax = "proto3";
+
+package monorail;
+
+import "api/api_proto/user_objects.proto";
+import "api/api_proto/common.proto";
+
+service Users {
+  rpc GetUser (GetUserRequest) returns (User) {}
+  rpc ListReferencedUsers (ListReferencedUsersRequest) returns (ListReferencedUsersResponse) {}
+  rpc GetMemberships (GetMembershipsRequest) returns (GetMembershipsResponse) {}
+  rpc GetSavedQueries (GetSavedQueriesRequest) returns (GetSavedQueriesResponse) {}
+  rpc GetUserStarCount (GetUserStarCountRequest) returns (GetUserStarCountResponse) {}
+  rpc StarUser (StarUserRequest) returns (StarUserResponse) {}
+  rpc GetUserPrefs (GetUserPrefsRequest) returns (GetUserPrefsResponse) {}
+  rpc SetUserPrefs (SetUserPrefsRequest) returns (SetUserPrefsResponse) {}
+  // TODO(jrobbins): Merge this into SetUserPrefs.
+  rpc SetExpandPermsPreference (SetExpandPermsPreferenceRequest) returns (SetExpandPermsPreferenceResponse) {}
+  rpc InviteLinkedParent (InviteLinkedParentRequest) returns (InviteLinkedParentResponse) {}
+  rpc AcceptLinkedChild (AcceptLinkedChildRequest) returns (AcceptLinkedChildResponse) {}
+  rpc UnlinkAccounts (UnlinkAccountsRequest) returns (UnlinkAccountsResponse) {}
+  rpc GetUsersProjects (GetUsersProjectsRequest) returns (GetUsersProjectsResponse) {}
+  rpc ExpungeUser (ExpungeUserRequest) returns (ExpungeUserResponse) {}
+}
+
+
+// Next available tag: 4
+message ListReferencedUsersRequest {
+  // emails is deprecated. Use user_refs instead.
+  repeated string emails = 2;
+  repeated UserRef user_refs = 3;
+}
+
+
+message ListReferencedUsersResponse {
+  repeated User users = 1;
+}
+
+
+// Next available tag: 3
+message GetUserRequest {
+  UserRef user_ref = 2;
+}
+
+
+// Next available tag: 3
+message GetMembershipsRequest {
+  UserRef user_ref = 2;
+}
+
+
+// Next available tag: 2
+message GetMembershipsResponse {
+  repeated UserRef group_refs = 1;
+}
+
+
+// Next available tag: 3
+message GetSavedQueriesRequest {
+  UserRef user_ref = 2;
+}
+
+
+// Next available tag: 2
+message GetSavedQueriesResponse {
+  repeated SavedQuery saved_queries = 1;
+}
+
+// Next available tag: 3
+message GetUserStarCountRequest {
+  UserRef user_ref = 2;
+}
+
+
+// Next available tag: 2
+message GetUserStarCountResponse {
+  uint32 star_count = 1;
+}
+
+
+// Next available tag: 4
+message StarUserRequest {
+  UserRef user_ref = 2;
+  bool starred = 3;
+}
+
+
+// Next available tag: 2
+message StarUserResponse {
+  uint32 star_count = 1;
+}
+
+
+// Next available tag: 3
+message SetExpandPermsPreferenceRequest {
+  bool expand_perms = 2;
+}
+
+
+// Next available tag: 1
+message SetExpandPermsPreferenceResponse {
+}
+
+
+// Next available tag: 3
+message GetUserPrefsRequest {
+  // Site admins may get prefs for specific users.  Otherwise, it gets
+  // prefs for the signed-in user.
+  UserRef user_ref = 2;
+}
+
+
+// Next available tag: 2
+message GetUserPrefsResponse {
+  repeated UserPrefValue prefs = 1;
+}
+
+
+// Next available tag: 5
+message SetUserPrefsRequest {
+  // Site admins may set prefs for specific users.  Otherwise, it sets
+  // prefs for the signed-in user.
+  UserRef user_ref = 2;
+  // The given prefs add to or overwrite current user prefs.
+  repeated UserPrefValue prefs = 3;
+}
+
+
+// Next available tag: 1
+message SetUserPrefsResponse {
+}
+
+
+// Next available tag: 3
+message InviteLinkedParentRequest {
+  string email = 2;
+}
+
+
+// Next available tag: 1
+message InviteLinkedParentResponse {
+}
+
+
+// Next available tag: 3
+message AcceptLinkedChildRequest {
+  string email = 2;
+}
+
+
+// Next available tag: 1
+message AcceptLinkedChildResponse {
+}
+
+
+// Next available tag: 4
+message UnlinkAccountsRequest {
+  UserRef parent = 2;
+  UserRef child = 3;
+}
+
+
+// Next available tag: 1
+message UnlinkAccountsResponse {
+}
+
+
+// Next available tag: 2
+message GetUsersProjectsRequest {
+  repeated UserRef user_refs = 1;
+}
+
+
+// Next available tag: 5
+message GetUsersProjectsResponse {
+  repeated UserProjects users_projects = 1;
+}
+
+
+// Next available tag: 2
+message ExpungeUserRequest {
+  string email = 1;
+}
+
+
+// Next available tag: 1
+message ExpungeUserResponse {
+}
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