diff --git a/lib/types/identity-search/auth-message-types.js b/lib/types/identity-search/auth-message-types.js
new file mode 100644
--- /dev/null
+++ b/lib/types/identity-search/auth-message-types.js
@@ -0,0 +1,21 @@
+// @flow
+
+import type { TInterface } from 'tcomb';
+import t from 'tcomb';
+
+import { tShape, tString } from '../../utils/validation-utils.js';
+
+export type AuthMessage = {
+  +type: 'AuthMessage',
+  +userID: string,
+  +deviceID: string,
+  +accessToken: string,
+};
+
+export const authMessageValidator: TInterface<AuthMessage> =
+  tShape<AuthMessage>({
+    type: tString('AuthMessage'),
+    userID: t.String,
+    deviceID: t.String,
+    accessToken: t.String,
+  });
diff --git a/lib/types/identity-search/messages.js b/lib/types/identity-search/messages.js
new file mode 100644
--- /dev/null
+++ b/lib/types/identity-search/messages.js
@@ -0,0 +1,71 @@
+// @flow
+
+import type { TUnion } from 'tcomb';
+import t from 'tcomb';
+
+import {
+  type AuthMessage,
+  authMessageValidator,
+} from './auth-message-types.js';
+import {
+  type SearchQuery,
+  searchQueryValidator,
+} from './search-query-types.js';
+import {
+  type SearchResponse,
+  searchResponseValidator,
+} from './search-response-types.js';
+import {
+  type ConnectionInitializationResponse,
+  connectionInitializationResponseValidator,
+} from '../websocket/connection-initialization-response-types.js';
+import {
+  type Heartbeat,
+  heartbeatValidator,
+} from '../websocket/heartbeat-types.js';
+
+/*
+ * This file defines types and validation for messages sent
+ * to Identity Search WebSocket server and messages sent to client.
+ * The definitions in this file should remain in sync
+ * with the structures defined in the corresponding
+ * Rust file at `shared/identity_search_messages/src/messages/mod.rs`.
+ *
+ * If you edit the definitions in one file,
+ * please make sure to update the corresponding definitions in the other.
+ *
+ */
+export const identitySearchMessageToClientTypes = Object.freeze({
+  CONNECTION_INITIALIZATION_RESPONSE: 'ConnectionInitializationResponse',
+  SUCCESS: 'Success',
+  ERROR: 'Error',
+  SEARCH_RESPONSE: 'SearchResponse',
+  HEARTBEAT: 'Heartbeat',
+});
+
+export const identitySearchMessageToClientValidator: TUnion<IdentitySearchMessageToClient> =
+  t.union([
+    connectionInitializationResponseValidator,
+    searchResponseValidator,
+    heartbeatValidator,
+  ]);
+
+export type IdentitySearchMessageToClient =
+  | ConnectionInitializationResponse
+  | SearchResponse
+  | Heartbeat;
+
+export const identitySearchMessageToServerTypes = Object.freeze({
+  AUTH_MESSAGE: 'AuthMessage',
+  SEARCH_QUERY: 'SearchQuery',
+  PREFIX: 'Prefix',
+  HEARTBEAT: 'Heartbeat',
+});
+
+export const identitySearchMessageToServerValidator: TUnion<IdentitySearchMessageToServer> =
+  t.union([authMessageValidator, searchQueryValidator, heartbeatValidator]);
+
+export type IdentitySearchMessageToServer =
+  | AuthMessage
+  | SearchQuery
+  | Heartbeat;
diff --git a/lib/types/identity-search/search-query-types.js b/lib/types/identity-search/search-query-types.js
new file mode 100644
--- /dev/null
+++ b/lib/types/identity-search/search-query-types.js
@@ -0,0 +1,33 @@
+// @flow
+
+import type { TInterface } from 'tcomb';
+import t from 'tcomb';
+
+import { tShape, tString } from '../../utils/validation-utils.js';
+
+export type SearchMethod = Prefix;
+
+export type Prefix = {
+  +type: 'Prefix',
+  +prefix: string,
+};
+
+export const prefixValidator: TInterface<Prefix> = tShape<Prefix>({
+  type: tString('Prefix'),
+  prefix: t.String,
+});
+
+export const searchMethodValidator: TInterface<Prefix> = prefixValidator;
+
+export type SearchQuery = {
+  +type: 'SearchQuery',
+  +id: string,
+  +searchMethod: SearchMethod,
+};
+
+export const searchQueryValidator: TInterface<SearchQuery> =
+  tShape<SearchQuery>({
+    type: tString('SearchQuery'),
+    id: t.String,
+    searchMethod: searchMethodValidator,
+  });
diff --git a/lib/types/identity-search/search-response-types.js b/lib/types/identity-search/search-response-types.js
new file mode 100644
--- /dev/null
+++ b/lib/types/identity-search/search-response-types.js
@@ -0,0 +1,53 @@
+// @flow
+
+import type { TInterface, TUnion } from 'tcomb';
+import t from 'tcomb';
+
+import { tShape, tString } from '../../utils/validation-utils.js';
+
+export type Failure = {
+  +id: string,
+  +error: string,
+};
+
+export const failureValidator: TInterface<Failure> = tShape<Failure>({
+  id: t.String,
+  error: t.String,
+});
+
+export type User = {
+  +userID: string,
+  +username: string,
+};
+
+export const userValidator: TInterface<User> = tShape<User>({
+  userID: t.String,
+  username: t.String,
+});
+
+export type SearchResult = {
+  +id: string,
+  +hits: $ReadOnlyArray<User>,
+};
+
+export const searchResultValidator: TInterface<SearchResult> =
+  tShape<SearchResult>({
+    id: t.String,
+    hits: t.list(userValidator),
+  });
+
+type SearchResponseSuccess = { +type: 'Success', +data: SearchResult };
+type SearchResponseError = { +type: 'Error', +data: Failure };
+
+export type SearchResponse = SearchResponseSuccess | SearchResponseError;
+
+export const searchResponseValidator: TUnion<SearchResponse> = t.union([
+  tShape<SearchResponseSuccess>({
+    type: tString('Success'),
+    data: searchResultValidator,
+  }),
+  tShape<SearchResponseError>({
+    type: tString('Error'),
+    data: failureValidator,
+  }),
+]);