diff --git a/lib/firebase.js b/lib/firebase.js
index 48df2287..917df680 100644
--- a/lib/firebase.js
+++ b/lib/firebase.js
@@ -24,15 +24,6 @@ import Utils, { statics as UtilsStatics } from './modules/utils';
 
 const FirebaseCoreModule = NativeModules.RNFirebase;
 
-export type FirebaseOptions = {
-  apiKey: string,
-  appId: string,
-  databaseURL: string,
-  messagingSenderId: string,
-  projectId: string,
-  storageBucket: string,
-}
-
 class FirebaseCore {
   _nativeEmitters: { [string]: NativeEventEmitter };
   _nativeSubscriptions: { [string]: boolean };
diff --git a/lib/flow.js b/lib/flow.js
index f5295758..71c478e8 100644
--- a/lib/flow.js
+++ b/lib/flow.js
@@ -1,20 +1,39 @@
 /* eslint-disable */
-// declare module 'react-native' {
-//   // noinspection ES6ConvertVarToLetConst
-//   declare var exports: any;
-// }
+/* Core types */
+declare class FirebaseError {
+  message: string,
+  name: string,
+  code: string,
+  stack: string,
+  path: string,
+  details: string,
+  modifiers: string
+};
 
-declare type AuthResultType = {
+declare type FirebaseOptions = {
+  apiKey: string,
+  appId: string,
+  databaseURL: string,
+  messagingSenderId: string,
+  projectId: string,
+  storageBucket: string,
+}
+
+/* Auth types */
+
+declare type AuthResult = {
   authenticated: boolean,
   user: Object|null
 } | null;
 
-declare type CredentialType = {
+declare type AuthCredential = {
   providerId: string,
   token: string,
   secret: string
 };
 
+/* Database types */
+
 declare type DatabaseListener = {
   listenerId: number;
   eventName: string;
@@ -31,6 +50,40 @@ declare type DatabaseModifier = {
   valueType?: string;
 };
 
+/* Firestore types */
+
+declare type FirestoreNativeDocumentChange = {
+  document: FirestoreNativeDocumentSnapshot,
+  newIndex: number,
+  oldIndex: number,
+  type: string,
+}
+
+declare type FirestoreNativeDocumentSnapshot = {
+  data: { [string]: FirestoreTypeMap },
+  metadata: FirestoreSnapshotMetadata,
+  path: string,
+}
+
+declare type FirestoreSnapshotMetadata = {
+  fromCache: boolean,
+  hasPendingWrites: boolean,
+}
+
+declare type FirestoreQueryDirection = 'DESC' | 'desc' | 'ASC' | 'asc';
+declare type FirestoreQueryOperator = '<' | '<=' | '=' | '==' | '>' | '>=';
+
+declare type FirestoreTypeMap = {
+  type: 'array' | 'boolean' | 'date' | 'fieldvalue' | 'geopoint' | 'null' | 'number' | 'object' | 'reference' | 'string',
+  value: any,
+}
+
+declare type FirestoreWriteOptions = {
+  merge?: boolean,
+}
+
+/* Util types */
+
 declare type GoogleApiAvailabilityType = {
   status: number,
   isAvailable: boolean,
@@ -38,13 +91,3 @@ declare type GoogleApiAvailabilityType = {
   hasResolution?: boolean,
   error?: string
 };
-
-declare class FirebaseError {
-  message: string,
-  name: string,
-  code: string,
-  stack: string,
-  path: string,
-  details: string,
-  modifiers: string
-};
diff --git a/lib/modules/auth/ConfirmationResult.js b/lib/modules/auth/ConfirmationResult.js
index 0c1c09b3..a2b80b72 100644
--- a/lib/modules/auth/ConfirmationResult.js
+++ b/lib/modules/auth/ConfirmationResult.js
@@ -1,8 +1,12 @@
 /**
- * @url https://firebase.google.com/docs/reference/js/firebase.User
+ * @flow
+ * ConfirmationResult representation wrapper
  */
+import type Auth from './';
+import type User from './User';
+
 export default class ConfirmationResult {
-  _auth: Object;
+  _auth: Auth;
   _verificationId: string;
 
   /**
@@ -10,7 +14,7 @@ export default class ConfirmationResult {
    * @param auth
    * @param verificationId The phone number authentication operation's verification ID.
    */
-  constructor(auth: Object, verificationId: string) {
+  constructor(auth: Auth, verificationId: string) {
     this._auth = auth;
     this._verificationId = verificationId;
   }
@@ -20,13 +24,11 @@ export default class ConfirmationResult {
    * @param verificationCode
    * @return {*}
    */
-  confirm(verificationCode: string): Promise<Object> {
-    return this._auth._interceptUserValue(
-      this._auth._native._confirmVerificationCode(verificationCode)
-    );
+  confirm(verificationCode: string): Promise<?User> {
+    return this._auth._interceptUserValue(this._auth._native._confirmVerificationCode(verificationCode));
   }
 
-  get verificationId(): String | null {
+  get verificationId(): string | null {
     return this._verificationId;
   }
 }
diff --git a/lib/modules/auth/PhoneAuthListener.js b/lib/modules/auth/PhoneAuthListener.js
index 620ad7f1..170aa370 100644
--- a/lib/modules/auth/PhoneAuthListener.js
+++ b/lib/modules/auth/PhoneAuthListener.js
@@ -2,6 +2,8 @@
 import INTERNALS from './../../internals';
 import { generatePushID, isFunction, isAndroid, isIOS, isString, nativeToJSError } from './../../utils';
 
+import type Auth from './';
+
 type PhoneAuthSnapshot = {
   state: 'sent' | 'timeout' | 'verified' | 'error',
   verificationId: string,
@@ -17,7 +19,6 @@ type PhoneAuthError = {
 };
 
 export default class PhoneAuthListener {
-
   _auth: Object;
   _timeout: number;
   _publicEvents: Object;
@@ -34,7 +35,7 @@ export default class PhoneAuthListener {
    * @param phoneNumber
    * @param timeout
    */
-  constructor(auth: Object, phoneNumber: string, timeout?: number) {
+  constructor(auth: Auth, phoneNumber: string, timeout?: number) {
     this._auth = auth;
     this._reject = null;
     this._resolve = null;
diff --git a/lib/modules/auth/Usera.js b/lib/modules/auth/User.js
similarity index 52%
rename from lib/modules/auth/Usera.js
rename to lib/modules/auth/User.js
index 50cbb024..026ce93d 100644
--- a/lib/modules/auth/Usera.js
+++ b/lib/modules/auth/User.js
@@ -1,104 +1,144 @@
+/**
+ * @flow
+ * User representation wrapper
+ */
 import INTERNALS from './../../internals';
 
-/**
- * @url https://firebase.google.com/docs/reference/js/firebase.User
- */
+import type Auth from './';
+
+type NativeUser = {
+  displayName?: string,
+  email?: string,
+  emailVerified?: boolean,
+  isAnonymous?: boolean,
+  phoneNumber?: string,
+  photoURL?: string,
+  providerData: UserInfo[],
+  providerId: string,
+  uid: string,
+}
+
+type UserInfo = {
+  displayName?: string,
+  email?: string,
+  phoneNumber?: string,
+  photoURL?: string,
+  providerId: string,
+  uid: string,
+}
+
 export default class User {
+  _auth: Auth;
+  _user: NativeUser;
+
   /**
    *
-   * @param authClass Instance of Authentication class
+   * @param auth Instance of Authentication class
    * @param user user result object from native
    */
-  constructor(authClass, userObj) {
-    this._auth = authClass;
-    this._user = userObj;
-  }
-
-  /**
-   * INTERNALS
-   */
-
-  /**
-   * Returns a user property or null if does not exist
-   * @param prop
-   * @returns {*}
-   * @private
-   */
-  _valueOrNull(prop) {
-    if (!Object.hasOwnProperty.call(this._user, prop)) return null;
-    return this._user[prop];
-  }
-
-  /**
-   * Returns a user property or false if does not exist
-   * @param prop
-   * @returns {*}
-   * @private
-   */
-  _valueOrFalse(prop) {
-    if (!Object.hasOwnProperty.call(this._user, prop)) return false;
-    return this._user[prop];
+  constructor(auth: Auth, user: NativeUser) {
+    this._auth = auth;
+    this._user = user;
   }
 
   /**
    * PROPERTIES
    */
 
-  get displayName(): String | null {
-    return this._valueOrNull('displayName');
+  get displayName(): ?string {
+    return this._user.displayName || null;
   }
 
-  get email(): String | null {
-    return this._valueOrNull('email');
+  get email(): ?string {
+    return this._user.email || null;
   }
 
-  get emailVerified(): Boolean {
-    return this._valueOrNull('emailVerified');
+  get emailVerified(): boolean {
+    return this._user.emailVerified || false;
   }
 
-  get isAnonymous(): Boolean {
-    return this._valueOrFalse('isAnonymous');
+  get isAnonymous(): boolean {
+    return this._user.isAnonymous || false;
   }
 
-  get phoneNumber(): String | null {
-    return this._valueOrNull('phoneNumber');
+  get phoneNumber(): ?string {
+    return this._user.phoneNumber || null;
   }
 
-  get photoURL(): String | null {
-    return this._valueOrNull('photoURL');
+  get photoURL(): ?string {
+    return this._user.photoURL || null;
   }
 
-  get providerId() {
-    return this._valueOrNull('providerId');
+  get providerData(): Array<UserInfo> {
+    return this._user.providerData;
   }
 
-  get uid(): String {
-    return this._valueOrNull('uid');
+  get providerId(): string {
+    return this._user.providerId;
+  }
+
+  get uid(): string {
+    return this._user.uid;
   }
 
-  // noinspection ReservedWordAsName
   /**
    * METHODS
    */
 
-  toJSON() {
-    return Object.assign({}, this._user);
-  }
-
   /**
    * Delete the current user
    * @return {Promise}
    */
-  delete(): Promise<Object> {
-    return this._auth._interceptUserValue(this._auth._native.delete());
+  delete(): Promise<void> {
+    return this._auth
+      ._interceptUndefinedUserValue(this._auth._native.delete());
+  }
+
+  /**
+   * get the token of current user
+   * @return {Promise}
+   */
+  getIdToken(forceRefresh: boolean = false): Promise<string> {
+    return this._auth._native.getToken(forceRefresh);
   }
 
   /**
    *
    * @param credential
    */
-  linkWithCredential(credential: CredentialType) {
-    return this._auth._interceptUserValue(this._auth._native.link(credential.providerId, credential.token, credential.secret));
+  linkWithCredential(credential: AuthCredential): Promise<User> {
+    return this._auth
+      ._interceptUserValue(this._auth._native.link(credential.providerId, credential.token, credential.secret));
+  }
+
+  /**
+   * Re-authenticate a user with a third-party authentication provider
+   * @return {Promise}         A promise resolved upon completion
+   */
+  reauthenticateWithCredential(credential: AuthCredential): Promise<void> {
+    return this._auth
+      ._interceptUndefinedUserValue(this._auth._native.reauthenticate(credential.providerId, credential.token, credential.secret));
+  }
+
+  /**
+   * Reload the current user
+   * @return {Promise}
+   */
+  reload(): Promise<void> {
+    return this._auth
+      ._interceptUndefinedUserValue(this._auth._native.reload());
+  }
+
+  /**
+   * Send verification email to current user.
+   */
+  sendEmailVerification(): Promise<void> {
+    return this._auth
+      ._interceptUndefinedUserValue(this._auth._native.sendEmailVerification());
+  }
+
+  toJSON(): Object {
+    return Object.assign({}, this._user);
   }
 
   /**
@@ -106,69 +146,19 @@ export default class User {
    * @param providerId
    * @return {Promise.<TResult>|*}
    */
-  unlink(providerId: string) {
+  unlink(providerId: string): Promise<User> {
     return this._auth._interceptUserValue(this._auth._native.unlink(providerId));
   }
 
-  /**
-   * Re-authenticate a user with a third-party authentication provider
-   * @return {Promise}         A promise resolved upon completion
-   */
-  reauthenticateWithCredential(credential: CredentialType) {
-    return this._auth._interceptUserValue(this._auth._native.reauthenticate(credential.providerId, credential.token, credential.secret));
-  }
-
-  /**
-   * Reload the current user
-   * @return {Promise}
-   */
-  reload(): Promise<Object> {
-    return this._auth._interceptUserValue(this._auth._native.reload());
-  }
-
-  /**
-   * get the token of current user
-   * @deprecated Deprecated getToken in favor of getIdToken.
-   * @return {Promise}
-   */
-  getToken(forceRefresh: Boolean = false): Promise<Object> {
-    console.warn('Deprecated firebase.User.prototype.getToken in favor of firebase.User.prototype.getIdToken.');
-    return this._auth._native.getToken(forceRefresh);
-  }
-
-  /**
-   * get the token of current user
-   * @return {Promise}
-   */
-  getIdToken(forceRefresh: Boolean = false): Promise<Object> {
-    return this._auth._native.getToken(forceRefresh);
-  }
-
-  /**
-   *
-   * @returns {Array}
-   */
-  get providerData(): Array {
-    return this._valueOrNull('providerData') || [];
-  }
-
   /**
    * Update the current user's email
    *
    * @param  {string} email The user's _new_ email
    * @return {Promise}       A promise resolved upon completion
    */
-  updateEmail(email: string): Promise<Object> {
-    return this._auth._interceptUserValue(this._auth._native.updateEmail(email));
-  }
-
-  /**
-   * Update the current user's profile
-   * @param  {Object} updates An object containing the keys listed [here](https://firebase.google.com/docs/auth/ios/manage-users#update_a_users_profile)
-   * @return {Promise}
-   */
-  updateProfile(updates: Object = {}): Promise<Object> {
-    return this._auth._interceptUserValue(this._auth._native.updateProfile(updates));
+  updateEmail(email: string): Promise<void> {
+    return this._auth
+      ._interceptUndefinedUserValue(this._auth._native.updateEmail(email));
   }
 
   /**
@@ -176,15 +166,29 @@ export default class User {
    * @param  {string} password the new password
    * @return {Promise}
    */
-  updatePassword(password: string): Promise<Object> {
-    return this._auth._interceptUserValue(this._auth._native.updatePassword(password));
+  updatePassword(password: string): Promise<void> {
+    return this._auth
+      ._interceptUndefinedUserValue(this._auth._native.updatePassword(password));
   }
 
   /**
-   * Send verification email to current user.
+   * Update the current user's profile
+   * @param  {Object} updates An object containing the keys listed [here](https://firebase.google.com/docs/auth/ios/manage-users#update_a_users_profile)
+   * @return {Promise}
    */
-  sendEmailVerification(): Promise<Object> {
-    return this._auth._interceptUserValue(this._auth._native.sendEmailVerification());
+  updateProfile(updates: Object = {}): Promise<void> {
+    return this._auth
+      ._interceptUndefinedUserValue(this._auth._native.updateProfile(updates));
+  }
+
+  /**
+   * get the token of current user
+   * @deprecated Deprecated getToken in favor of getIdToken.
+   * @return {Promise}
+   */
+  getToken(forceRefresh: boolean = false): Promise<Object> {
+    console.warn('Deprecated firebase.User.prototype.getToken in favor of firebase.User.prototype.getIdToken.');
+    return this._auth._native.getToken(forceRefresh);
   }
 
   /**
@@ -223,7 +227,7 @@ export default class User {
     throw new Error(INTERNALS.STRINGS.ERROR_UNSUPPORTED_CLASS_METHOD('User', 'updatePhoneNumber'));
   }
 
-  get refreshToken() {
+  get refreshToken(): string {
     throw new Error(INTERNALS.STRINGS.ERROR_UNSUPPORTED_CLASS_PROPERTY('User', 'refreshToken'));
   }
 }
diff --git a/lib/modules/auth/index.js b/lib/modules/auth/index.js
index 378a23aa..fcd42b59 100644
--- a/lib/modules/auth/index.js
+++ b/lib/modules/auth/index.js
@@ -1,5 +1,8 @@
-// @flow
-import User from './user';
+/**
+ * @flow
+ * Auth representation wrapper
+ */
+import User from './User';
 import ModuleBase from './../../utils/ModuleBase';
 import INTERNALS from './../../internals';
 import ConfirmationResult from './ConfirmationResult';
@@ -14,16 +17,16 @@ import FacebookAuthProvider from './providers/FacebookAuthProvider';
 
 import PhoneAuthListener from './PhoneAuthListener';
 
+import type FirebaseApp from '../../firebase-app';
+
 export default class Auth extends ModuleBase {
   static _NAMESPACE = 'auth';
   static _NATIVE_MODULE = 'RNFirebaseAuth';
 
+  _authResult: AuthResult | null;
   _user: User | null;
-  _native: Object;
-  _getAppEventName: Function;
-  _authResult: AuthResultType | null;
 
-  constructor(firebaseApp: Object, options: Object = {}) {
+  constructor(firebaseApp: FirebaseApp, options: Object = {}) {
     super(firebaseApp, options, true);
     this._user = null;
     this._authResult = null;
@@ -31,21 +34,21 @@ export default class Auth extends ModuleBase {
     this.addListener(
       // sub to internal native event - this fans out to
       // public event name: onAuthStateChanged
-      this._getAppEventName('auth_state_changed'),
+      super._getAppEventName('auth_state_changed'),
       this._onInternalAuthStateChanged.bind(this),
     );
 
     this.addListener(
       // sub to internal native event - this fans out to
       // public events based on event.type
-      this._getAppEventName('phone_auth_state_changed'),
+      super._getAppEventName('phone_auth_state_changed'),
       this._onInternalPhoneAuthStateChanged.bind(this),
     );
 
     this.addListener(
       // sub to internal native event - this fans out to
       // public event name: onIdTokenChanged
-      this._getAppEventName('auth_id_token_changed'),
+      super._getAppEventName('auth_id_token_changed'),
       this._onInternalIdTokenChanged.bind(this),
     );
 
@@ -63,7 +66,7 @@ export default class Auth extends ModuleBase {
     this.emit(eventKey, event.state);
   }
 
-  _setAuthState(auth: AuthResultType) {
+  _setAuthState(auth: AuthResult) {
     this._authResult = auth;
     this._user = auth && auth.user ? new User(this, auth.user) : null;
     this.emit(this._getAppEventName('onUserChanged'), this._user);
@@ -74,7 +77,7 @@ export default class Auth extends ModuleBase {
    * @param auth
    * @private
    */
-  _onInternalAuthStateChanged(auth: AuthResultType) {
+  _onInternalAuthStateChanged(auth: AuthResult) {
     this._setAuthState(auth);
     this.emit(this._getAppEventName('onAuthStateChanged'), this._user);
   }
@@ -85,7 +88,7 @@ export default class Auth extends ModuleBase {
    * @param emit
    * @private
    */
-  _onInternalIdTokenChanged(auth: AuthResultType) {
+  _onInternalIdTokenChanged(auth: AuthResult) {
     this._setAuthState(auth);
     this.emit(this._getAppEventName('onIdTokenChanged'), this._user);
   }
@@ -97,8 +100,8 @@ export default class Auth extends ModuleBase {
    * @returns {Promise.<*>}
    * @private
    */
-  _interceptUserValue(promise) {
-    return promise.then((result) => {
+  _interceptUserValue(promise: Promise<AuthResult>): Promise<User> {
+    return promise.then((result: AuthResult) => {
       if (!result) this._setAuthState(null);
       else if (result.user) this._setAuthState(result);
       else if (result.uid) this._setAuthState({ authenticated: true, user: result });
@@ -106,6 +109,11 @@ export default class Auth extends ModuleBase {
     });
   }
 
+  _interceptUndefinedUserValue(promise: Promise<AuthResult>): Promise<void> {
+    return this._interceptUserValue(promise)
+      .then(() => {});
+  }
+
   /*
    * WEB API
    */
@@ -174,15 +182,15 @@ export default class Auth extends ModuleBase {
    * Sign the current user out
    * @return {Promise}
    */
-  signOut(): Promise<null> {
-    return this._interceptUserValue(this._native.signOut());
+  signOut(): Promise<void> {
+    return this._interceptUndefinedUserValue(this._native.signOut());
   }
 
   /**
    * Sign a user in anonymously
    * @return {Promise} A promise resolved upon completion
    */
-  signInAnonymously(): Promise<Object> {
+  signInAnonymously(): Promise<User> {
     return this._interceptUserValue(this._native.signInAnonymously());
   }
 
@@ -192,7 +200,7 @@ export default class Auth extends ModuleBase {
    * @param  {string} password The user's password
    * @return {Promise}         A promise indicating the completion
    */
-  createUserWithEmailAndPassword(email: string, password: string): Promise<Object> {
+  createUserWithEmailAndPassword(email: string, password: string): Promise<User> {
     return this._interceptUserValue(this._native.createUserWithEmailAndPassword(email, password));
   }
 
@@ -202,7 +210,7 @@ export default class Auth extends ModuleBase {
    * @param  {string} password The user's password
    * @return {Promise}         A promise that is resolved upon completion
    */
-  signInWithEmailAndPassword(email: string, password: string): Promise<Object> {
+  signInWithEmailAndPassword(email: string, password: string): Promise<User> {
     return this._interceptUserValue(this._native.signInWithEmailAndPassword(email, password));
   }
 
@@ -211,7 +219,7 @@ export default class Auth extends ModuleBase {
    * @param  {string} customToken  A self-signed custom auth token.
    * @return {Promise}             A promise resolved upon completion
    */
-  signInWithCustomToken(customToken: string): Promise<Object> {
+  signInWithCustomToken(customToken: string): Promise<User> {
     return this._interceptUserValue(this._native.signInWithCustomToken(customToken));
   }
 
@@ -219,7 +227,7 @@ export default class Auth extends ModuleBase {
    * Sign the user in with a third-party authentication provider
    * @return {Promise}           A promise resolved upon completion
    */
-  signInWithCredential(credential: CredentialType): Promise<Object> {
+  signInWithCredential(credential: AuthCredential): Promise<User> {
     return this._interceptUserValue(
       this._native.signInWithCredential(
         credential.providerId, credential.token, credential.secret,
@@ -231,7 +239,7 @@ export default class Auth extends ModuleBase {
    * Asynchronously signs in using a phone number.
    *
    */
-  signInWithPhoneNumber(phoneNumber: string): Promise<Object> {
+  signInWithPhoneNumber(phoneNumber: string): Promise<ConfirmationResult> {
     return this._native.signInWithPhoneNumber(phoneNumber).then((result) => {
       return new ConfirmationResult(this, result.verificationId);
     });
@@ -254,7 +262,7 @@ export default class Auth extends ModuleBase {
    * Send reset password instructions via email
    * @param {string} email The email to send password reset instructions
    */
-  sendPasswordResetEmail(email: string): Promise<Object> {
+  sendPasswordResetEmail(email: string): Promise<void> {
     return this._native.sendPasswordResetEmail(email);
   }
 
@@ -266,7 +274,7 @@ export default class Auth extends ModuleBase {
    * @param newPassword
    * @return {Promise.<Null>}
    */
-  confirmPasswordReset(code: string, newPassword: string): Promise<null> {
+  confirmPasswordReset(code: string, newPassword: string): Promise<void> {
     return this._native.confirmPasswordReset(code, newPassword);
   }
 
@@ -277,7 +285,7 @@ export default class Auth extends ModuleBase {
    * @param code
    * @return {Promise.<Null>}
    */
-  applyActionCode(code: string): Promise<any> {
+  applyActionCode(code: string): Promise<void> {
     return this._native.applyActionCode(code);
   }
 
@@ -288,7 +296,7 @@ export default class Auth extends ModuleBase {
    * @param code
    * @return {Promise.<any>|Promise<ActionCodeInfo>}
    */
-  checkActionCode(code: string): Promise<any> {
+  checkActionCode(code: string): Promise<void> {
     return this._native.checkActionCode(code);
   }
 
@@ -296,7 +304,7 @@ export default class Auth extends ModuleBase {
    * Get the currently signed in user
    * @return {Promise}
    */
-  getCurrentUser(): Promise<Object> {
+  getCurrentUser(): Promise<User | null> {
     return this._interceptUserValue(this._native.getCurrentUser());
   }
 
diff --git a/lib/modules/auth/providers/EmailAuthProvider.js b/lib/modules/auth/providers/EmailAuthProvider.js
index d4175aba..b995687f 100644
--- a/lib/modules/auth/providers/EmailAuthProvider.js
+++ b/lib/modules/auth/providers/EmailAuthProvider.js
@@ -1,3 +1,7 @@
+/**
+ * @flow
+ * EmailAuthProvider representation wrapper
+ */
 const providerId = 'password';
 
 export default class EmailAuthProvider {
@@ -5,11 +9,11 @@ export default class EmailAuthProvider {
     throw new Error('`new EmailAuthProvider()` is not supported on the native Firebase SDKs.');
   }
 
-  static get PROVIDER_ID() {
+  static get PROVIDER_ID(): string {
     return providerId;
   }
 
-  static credential(email, password) {
+  static credential(email: string, password: string): AuthCredential {
     return {
       token: email,
       secret: password,
diff --git a/lib/modules/auth/providers/FacebookAuthProvider.js b/lib/modules/auth/providers/FacebookAuthProvider.js
index c8abbc10..b60bf027 100644
--- a/lib/modules/auth/providers/FacebookAuthProvider.js
+++ b/lib/modules/auth/providers/FacebookAuthProvider.js
@@ -1,3 +1,7 @@
+/**
+ * @flow
+ * FacebookAuthProvider representation wrapper
+ */
 const providerId = 'facebook.com';
 
 export default class FacebookAuthProvider {
@@ -5,11 +9,11 @@ export default class FacebookAuthProvider {
     throw new Error('`new FacebookAuthProvider()` is not supported on the native Firebase SDKs.');
   }
 
-  static get PROVIDER_ID() {
+  static get PROVIDER_ID(): string {
     return providerId;
   }
 
-  static credential(token) {
+  static credential(token: string): AuthCredential {
     return {
       token,
       secret: '',
diff --git a/lib/modules/auth/providers/GithubAuthProvider.js b/lib/modules/auth/providers/GithubAuthProvider.js
index fbd84272..4500ce40 100644
--- a/lib/modules/auth/providers/GithubAuthProvider.js
+++ b/lib/modules/auth/providers/GithubAuthProvider.js
@@ -1,3 +1,7 @@
+/**
+ * @flow
+ * GithubAuthProvider representation wrapper
+ */
 const providerId = 'github.com';
 
 export default class GithubAuthProvider {
@@ -5,11 +9,11 @@ export default class GithubAuthProvider {
     throw new Error('`new GithubAuthProvider()` is not supported on the native Firebase SDKs.');
   }
 
-  static get PROVIDER_ID() {
+  static get PROVIDER_ID(): string {
     return providerId;
   }
 
-  static credential(token) {
+  static credential(token: string): AuthCredential {
     return {
       token,
       secret: '',
diff --git a/lib/modules/auth/providers/GoogleAuthProvider.js b/lib/modules/auth/providers/GoogleAuthProvider.js
index eda9f241..717aa0ce 100644
--- a/lib/modules/auth/providers/GoogleAuthProvider.js
+++ b/lib/modules/auth/providers/GoogleAuthProvider.js
@@ -1,3 +1,7 @@
+/**
+ * @flow
+ * EmailAuthProvider representation wrapper
+ */
 const providerId = 'google.com';
 
 export default class GoogleAuthProvider {
@@ -5,11 +9,11 @@ export default class GoogleAuthProvider {
     throw new Error('`new GoogleAuthProvider()` is not supported on the native Firebase SDKs.');
   }
 
-  static get PROVIDER_ID() {
+  static get PROVIDER_ID(): string {
     return providerId;
   }
 
-  static credential(token, secret) {
+  static credential(token: string, secret: string): AuthCredential {
     return {
       token,
       secret,
diff --git a/lib/modules/auth/providers/PhoneAuthProvider.js b/lib/modules/auth/providers/PhoneAuthProvider.js
index 5186f009..6ac1cc57 100644
--- a/lib/modules/auth/providers/PhoneAuthProvider.js
+++ b/lib/modules/auth/providers/PhoneAuthProvider.js
@@ -1,3 +1,7 @@
+/**
+ * @flow
+ * PhoneAuthProvider representation wrapper
+ */
 const providerId = 'phone';
 
 export default class PhoneAuthProvider {
@@ -5,11 +9,11 @@ export default class PhoneAuthProvider {
     throw new Error('`new PhoneAuthProvider()` is not supported on the native Firebase SDKs.');
   }
 
-  static get PROVIDER_ID() {
+  static get PROVIDER_ID(): string {
     return providerId;
   }
 
-  static credential(verificationId, code) {
+  static credential(verificationId: string, code: string): AuthCredential {
     return {
       token: verificationId,
       secret: code,
diff --git a/lib/modules/auth/providers/TwitterAuthProvider.js b/lib/modules/auth/providers/TwitterAuthProvider.js
index 15c0a2f6..7f6cf902 100644
--- a/lib/modules/auth/providers/TwitterAuthProvider.js
+++ b/lib/modules/auth/providers/TwitterAuthProvider.js
@@ -1,3 +1,7 @@
+/**
+ * @flow
+ * TwitterAuthProvider representation wrapper
+ */
 const providerId = 'twitter.com';
 
 export default class TwitterAuthProvider {
@@ -5,11 +9,11 @@ export default class TwitterAuthProvider {
     throw new Error('`new TwitterAuthProvider()` is not supported on the native Firebase SDKs.');
   }
 
-  static get PROVIDER_ID() {
+  static get PROVIDER_ID(): string {
     return providerId;
   }
 
-  static credential(token, secret) {
+  static credential(token: string, secret: string): AuthCredential {
     return {
       token,
       secret,
diff --git a/lib/modules/firestore/CollectionReference.js b/lib/modules/firestore/CollectionReference.js
index 9c46eda2..6a906be9 100644
--- a/lib/modules/firestore/CollectionReference.js
+++ b/lib/modules/firestore/CollectionReference.js
@@ -3,7 +3,7 @@
  * CollectionReference representation wrapper
  */
 import DocumentReference from './DocumentReference';
-import Query, { type Direction, type Operator } from './Query';
+import Query from './Query';
 import { firestoreAutoId } from '../../utils';
 
 import type Firestore from './';
@@ -75,7 +75,7 @@ export default class CollectionReference {
     return this._query.onSnapshot(onNext, onError);
   }
 
-  orderBy(fieldPath: string, directionStr?: Direction): Query {
+  orderBy(fieldPath: string, directionStr?: FirestoreQueryDirection): Query {
     return this._query.orderBy(fieldPath, directionStr);
   }
 
@@ -87,7 +87,7 @@ export default class CollectionReference {
     return this._query.startAt(fieldValues);
   }
 
-  where(fieldPath: string, opStr: Operator, value: any): Query {
+  where(fieldPath: string, opStr: FirestoreQueryOperator, value: any): Query {
     return this._query.where(fieldPath, opStr, value);
   }
 }
diff --git a/lib/modules/firestore/DocumentChange.js b/lib/modules/firestore/DocumentChange.js
index b712aa7a..ffcda39d 100644
--- a/lib/modules/firestore/DocumentChange.js
+++ b/lib/modules/firestore/DocumentChange.js
@@ -2,18 +2,10 @@
  * @flow
  * DocumentChange representation wrapper
  */
-import DocumentSnapshot, { type DocumentSnapshotNativeData } from './DocumentSnapshot';
+import DocumentSnapshot from './DocumentSnapshot';
 
 import type Firestore from './';
 
-
-export type DocumentChangeNativeData = {
-  document: DocumentSnapshotNativeData,
-  newIndex: number,
-  oldIndex: number,
-  type: string,
-}
-
 /**
  * @class DocumentChange
  */
@@ -23,7 +15,7 @@ export default class DocumentChange {
   _oldIndex: number;
   _type: string;
 
-  constructor(firestore: Firestore, nativeData: DocumentChangeNativeData) {
+  constructor(firestore: Firestore, nativeData: FirestoreNativeDocumentChange) {
     this._document = new DocumentSnapshot(firestore, nativeData.document);
     this._newIndex = nativeData.newIndex;
     this._oldIndex = nativeData.oldIndex;
diff --git a/lib/modules/firestore/DocumentReference.js b/lib/modules/firestore/DocumentReference.js
index b6a703ed..aff4d304 100644
--- a/lib/modules/firestore/DocumentReference.js
+++ b/lib/modules/firestore/DocumentReference.js
@@ -3,17 +3,13 @@
  * DocumentReference representation wrapper
  */
 import CollectionReference from './CollectionReference';
-import DocumentSnapshot, { type DocumentSnapshotNativeData } from './DocumentSnapshot';
+import DocumentSnapshot from './DocumentSnapshot';
 import { buildNativeMap } from './utils/serialize';
 import { firestoreAutoId, isFunction, isObject, isString } from '../../utils';
 
 import type Firestore from './';
 import type Path from './Path';
 
-export type WriteOptions = {
-  merge?: boolean,
-}
-
 type DocumentListenOptions = {
   includeMetadataChanges: boolean,
 }
@@ -133,7 +129,7 @@ export default class DocumentReference {
     }
     const listenerId = firestoreAutoId();
 
-    const listener = (nativeDocumentSnapshot: DocumentSnapshotNativeData) => {
+    const listener = (nativeDocumentSnapshot: FirestoreNativeDocumentSnapshot) => {
       const documentSnapshot = new DocumentSnapshot(this.firestore, nativeDocumentSnapshot);
       observer.next(documentSnapshot);
     };
@@ -160,7 +156,7 @@ export default class DocumentReference {
     return this._offDocumentSnapshot.bind(this, listenerId, listener);
   }
 
-  set(data: Object, writeOptions?: WriteOptions): Promise<void> {
+  set(data: Object, writeOptions?: FirestoreWriteOptions): Promise<void> {
     const nativeData = buildNativeMap(data);
     return this._firestore._native
       .documentSet(this.path, nativeData, writeOptions);
diff --git a/lib/modules/firestore/DocumentSnapshot.js b/lib/modules/firestore/DocumentSnapshot.js
index 35899c47..ab2bb378 100644
--- a/lib/modules/firestore/DocumentSnapshot.js
+++ b/lib/modules/firestore/DocumentSnapshot.js
@@ -4,30 +4,19 @@
  */
 import DocumentReference from './DocumentReference';
 import Path from './Path';
-import { parseNativeMap, type TypeMap } from './utils/serialize';
+import { parseNativeMap } from './utils/serialize';
 
 import type Firestore from './';
 
-export type SnapshotMetadata = {
-  fromCache: boolean,
-  hasPendingWrites: boolean,
-}
-
-export type DocumentSnapshotNativeData = {
-  data: { [string]: TypeMap },
-  metadata: SnapshotMetadata,
-  path: string,
-}
-
 /**
  * @class DocumentSnapshot
  */
 export default class DocumentSnapshot {
   _data: Object | void;
-  _metadata: SnapshotMetadata;
+  _metadata: FirestoreSnapshotMetadata;
   _ref: DocumentReference;
 
-  constructor(firestore: Firestore, nativeData: DocumentSnapshotNativeData) {
+  constructor(firestore: Firestore, nativeData: FirestoreNativeDocumentSnapshot) {
     this._data = parseNativeMap(firestore, nativeData.data);
     this._metadata = nativeData.metadata;
     this._ref = new DocumentReference(firestore, Path.fromName(nativeData.path));
@@ -41,7 +30,7 @@ export default class DocumentSnapshot {
     return this._ref.id;
   }
 
-  get metadata(): SnapshotMetadata {
+  get metadata(): FirestoreSnapshotMetadata {
     return this._metadata;
   }
 
diff --git a/lib/modules/firestore/Query.js b/lib/modules/firestore/Query.js
index 26bd0b22..81561b47 100644
--- a/lib/modules/firestore/Query.js
+++ b/lib/modules/firestore/Query.js
@@ -10,14 +10,14 @@ import { firestoreAutoId, isFunction, isObject } from '../../utils';
 import type Firestore from './';
 import type Path from './Path';
 
-const DIRECTIONS = {
+const DIRECTIONS: { [FirestoreQueryDirection]: string } = {
   ASC: 'ASCENDING',
   asc: 'ASCENDING',
   DESC: 'DESCENDING',
   desc: 'DESCENDING',
 };
 
-const OPERATORS = {
+const OPERATORS: { [FirestoreQueryOperator]: string } = {
   '=': 'EQUAL',
   '==': 'EQUAL',
   '>': 'GREATER_THAN',
@@ -26,7 +26,6 @@ const OPERATORS = {
   '<=': 'LESS_THAN_OR_EQUAL',
 };
 
-export type Direction = 'DESC' | 'desc' | 'ASC' | 'asc';
 type FieldFilter = {
   fieldPath: string,
   operator: string,
@@ -45,7 +44,6 @@ type QueryOptions = {
   startAfter?: any[],
   startAt?: any[],
 }
-export type Operator = '<' | '<=' | '=' | '==' | '>' | '>=';
 type QueryListenOptions = {
   includeDocumentMetadataChanges: boolean,
   includeQueryMetadataChanges: boolean,
@@ -234,7 +232,7 @@ export default class Query {
     return this._offCollectionSnapshot.bind(this, listenerId, listener);
   }
 
-  orderBy(fieldPath: string, directionStr?: Direction = 'asc'): Query {
+  orderBy(fieldPath: string, directionStr?: FirestoreQueryDirection = 'asc'): Query {
     // TODO: Validation
     // validate.isFieldPath('fieldPath', fieldPath);
     // validate.isOptionalFieldOrder('directionStr', directionStr);
@@ -288,7 +286,7 @@ export default class Query {
     );
   }
 
-  where(fieldPath: string, opStr: Operator, value: any): Query {
+  where(fieldPath: string, opStr: FirestoreQueryOperator, value: any): Query {
     // TODO: Validation
     // validate.isFieldPath('fieldPath', fieldPath);
     // validate.isFieldFilter('fieldFilter', opStr, value);
diff --git a/lib/modules/firestore/QuerySnapshot.js b/lib/modules/firestore/QuerySnapshot.js
index c7759b22..659815aa 100644
--- a/lib/modules/firestore/QuerySnapshot.js
+++ b/lib/modules/firestore/QuerySnapshot.js
@@ -2,16 +2,16 @@
  * @flow
  * QuerySnapshot representation wrapper
  */
-import DocumentChange, { type DocumentChangeNativeData } from './DocumentChange';
-import DocumentSnapshot, { type DocumentSnapshotNativeData, type SnapshotMetadata } from './DocumentSnapshot';
+import DocumentChange from './DocumentChange';
+import DocumentSnapshot from './DocumentSnapshot';
 
 import type Firestore from './';
 import type Query from './Query';
 
 type QuerySnapshotNativeData = {
-  changes: DocumentChangeNativeData[],
-  documents: DocumentSnapshotNativeData[],
-  metadata: SnapshotMetadata,
+  changes: FirestoreNativeDocumentChange[],
+  documents: FirestoreNativeDocumentSnapshot[],
+  metadata: FirestoreSnapshotMetadata,
 }
 
 /**
@@ -20,7 +20,7 @@ type QuerySnapshotNativeData = {
 export default class QuerySnapshot {
   _changes: DocumentChange[];
   _docs: DocumentSnapshot[];
-  _metadata: SnapshotMetadata;
+  _metadata: FirestoreSnapshotMetadata;
   _query: Query;
 
   constructor(firestore: Firestore, query: Query, nativeData: QuerySnapshotNativeData) {
@@ -42,7 +42,7 @@ export default class QuerySnapshot {
     return this._docs.length === 0;
   }
 
-  get metadata(): SnapshotMetadata {
+  get metadata(): FirestoreSnapshotMetadata {
     return this._metadata;
   }
 
diff --git a/lib/modules/firestore/WriteBatch.js b/lib/modules/firestore/WriteBatch.js
index 70771124..77318c3c 100644
--- a/lib/modules/firestore/WriteBatch.js
+++ b/lib/modules/firestore/WriteBatch.js
@@ -5,7 +5,7 @@
 import { buildNativeMap } from './utils/serialize';
 import { isObject, isString } from '../../utils';
 
-import type DocumentReference, { WriteOptions } from './DocumentReference';
+import type DocumentReference from './DocumentReference';
 import type Firestore from './';
 
 type DocumentWrite = {
@@ -44,7 +44,7 @@ export default class WriteBatch {
     return this;
   }
 
-  set(docRef: DocumentReference, data: Object, writeOptions?: WriteOptions) {
+  set(docRef: DocumentReference, data: Object, writeOptions?: FirestoreWriteOptions) {
     // TODO: Validation
     // validate.isDocumentReference('docRef', docRef);
     // validate.isDocument('data', data);
diff --git a/lib/modules/firestore/utils/serialize.js b/lib/modules/firestore/utils/serialize.js
index 4657711c..74fd2697 100644
--- a/lib/modules/firestore/utils/serialize.js
+++ b/lib/modules/firestore/utils/serialize.js
@@ -10,18 +10,13 @@ import { typeOf } from '../../../utils';
 
 import type Firestore from '../';
 
-export type TypeMap = {
-  type: 'array' | 'boolean' | 'date' | 'fieldvalue' | 'geopoint' | 'null' | 'number' | 'object' | 'reference' | 'string',
-  value: any,
-}
-
 /*
  * Functions that build up the data needed to represent
  * the different types available within Firestore
  * for transmission to the native side
  */
 
-export const buildNativeMap = (data: Object): { [string]: TypeMap } => {
+export const buildNativeMap = (data: Object): { [string]: FirestoreTypeMap } => {
   const nativeData = {};
   if (data) {
     Object.keys(data).forEach((key) => {
@@ -34,7 +29,7 @@ export const buildNativeMap = (data: Object): { [string]: TypeMap } => {
   return nativeData;
 };
 
-export const buildNativeArray = (array: Object[]): TypeMap[] => {
+export const buildNativeArray = (array: Object[]): FirestoreTypeMap[] => {
   const nativeArray = [];
   if (array) {
     array.forEach((value) => {
@@ -47,7 +42,7 @@ export const buildNativeArray = (array: Object[]): TypeMap[] => {
   return nativeArray;
 };
 
-export const buildTypeMap = (value: any): TypeMap | null => {
+export const buildTypeMap = (value: any): FirestoreTypeMap | null => {
   const type = typeOf(value);
   if (value === null || value === undefined) {
     return {
@@ -108,7 +103,7 @@ export const buildTypeMap = (value: any): TypeMap | null => {
  * side and converts to the correct Firestore JS types
  */
 
-export const parseNativeMap = (firestore: Firestore, nativeData: { [string]: TypeMap }): Object | void => {
+export const parseNativeMap = (firestore: Firestore, nativeData: { [string]: FirestoreTypeMap }): Object | void => {
   let data;
   if (nativeData) {
     data = {};
@@ -119,7 +114,7 @@ export const parseNativeMap = (firestore: Firestore, nativeData: { [string]: Typ
   return data;
 };
 
-const parseNativeArray = (firestore: Firestore, nativeArray: TypeMap[]): any[] => {
+const parseNativeArray = (firestore: Firestore, nativeArray: FirestoreTypeMap[]): any[] => {
   const array = [];
   if (nativeArray) {
     nativeArray.forEach((typeMap) => {
@@ -129,7 +124,7 @@ const parseNativeArray = (firestore: Firestore, nativeArray: TypeMap[]): any[] =
   return array;
 };
 
-const parseTypeMap = (firestore: Firestore, typeMap: TypeMap): any => {
+const parseTypeMap = (firestore: Firestore, typeMap: FirestoreTypeMap): any => {
   const { type, value } = typeMap;
   if (type === 'null') {
     return null;