diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
index 098c2514a7..76111ff428 100644
--- a/wp-includes/default-filters.php
+++ b/wp-includes/default-filters.php
@@ -342,6 +342,7 @@ add_filter( 'heartbeat_nopriv_send', 'wp_auth_check' );
 
 // Default authentication filters
 add_filter( 'authenticate', 'wp_authenticate_username_password',  20, 3 );
+add_filter( 'authenticate', 'wp_authenticate_email_password',     20, 3 );
 add_filter( 'authenticate', 'wp_authenticate_spam_check',         99    );
 add_filter( 'determine_current_user', 'wp_validate_auth_cookie'          );
 add_filter( 'determine_current_user', 'wp_validate_logged_in_cookie', 20 );
diff --git a/wp-includes/pluggable.php b/wp-includes/pluggable.php
index 8e24100a75..860d8027df 100644
--- a/wp-includes/pluggable.php
+++ b/wp-includes/pluggable.php
@@ -548,7 +548,7 @@ if ( !function_exists('wp_authenticate') ) :
  *
  * @since 2.5.0
  *
- * @param string $username User's username.
+ * @param string $username User's username or email address.
  * @param string $password User's password.
  * @return WP_User|WP_Error WP_User object if the credentials are valid,
  *                          otherwise WP_Error.
@@ -575,7 +575,7 @@ function wp_authenticate($username, $password) {
 	if ( $user == null ) {
 		// TODO what should the error message be? (Or would these even happen?)
 		// Only needed if all authentication handlers fail to return anything.
-		$user = new WP_Error('authentication_failed', __('<strong>ERROR</strong>: Invalid username or incorrect password.'));
+		$user = new WP_Error( 'authentication_failed', __( '<strong>ERROR</strong>: Invalid username, email address or incorrect password.' ) );
 	}
 
 	$ignore_codes = array('empty_username', 'empty_password');
diff --git a/wp-includes/user.php b/wp-includes/user.php
index c1c63045e3..8b1b0321b4 100644
--- a/wp-includes/user.php
+++ b/wp-includes/user.php
@@ -173,6 +173,78 @@ function wp_authenticate_username_password($user, $username, $password) {
 	return $user;
 }
 
+/**
+ * Authenticate the user using the email and password.
+ *
+ * @since 4.5.0
+ *
+ * @param WP_User|WP_Error|null $user     WP_User or WP_Error object if a previous
+ *                                        callback failed authentication.
+ * @param string                $email    Email address for authentication.
+ * @param string                $password Password for authentication.
+ * @return WP_User|WP_Error WP_User on success, WP_Error on failure.
+ */
+function wp_authenticate_email_password( $user, $email, $password ) {
+	if ( $user instanceof WP_User ) {
+		return $user;
+	}
+
+	if ( empty( $email ) || empty( $password ) ) {
+		if ( is_wp_error( $user ) ) {
+			return $user;
+		}
+
+		$error = new WP_Error();
+
+		if ( empty( $email ) ) {
+			$error->add( 'empty_username', __( '<strong>ERROR</strong>: The email field is empty.' ) ); // Uses 'empty_username' for back-compat with wp_signon()
+		}
+
+		if ( empty( $password ) ) {
+			$error->add( 'empty_password', __( '<strong>ERROR</strong>: The password field is empty.' ) );
+		}
+
+		return $error;
+	}
+
+	if ( ! is_email( $email ) ) {
+		return $user;
+	}
+
+	$user = get_user_by( 'email', $email );
+
+	if ( ! $user ) {
+		return new WP_Error( 'invalid_email',
+			__( '<strong>ERROR</strong>: Invalid email address.' ) .
+			' <a href="' . wp_lostpassword_url() . '">' .
+			__( 'Lost your password?' ) .
+			'</a>'
+		);
+	}
+
+	/** This filter is documented in wp-includes/user.php */
+	$user = apply_filters( 'wp_authenticate_user', $user, $password );
+
+	if ( is_wp_error( $user ) ) {
+		return $user;
+	}
+
+	if ( ! wp_check_password( $password, $user->user_pass, $user->ID ) ) {
+		return new WP_Error( 'incorrect_password',
+			sprintf(
+				/* translators: %s: email address */
+				__( '<strong>ERROR</strong>: The password you entered for the email address %s is incorrect.' ),
+				'<strong>' . $email . '</strong>'
+			) .
+			' <a href="' . wp_lostpassword_url() . '">' .
+			__( 'Lost your password?' ) .
+			'</a>'
+		);
+	}
+
+	return $user;
+}
+
 /**
  * Authenticate the user using the WordPress auth cookie.
  *
diff --git a/wp-includes/version.php b/wp-includes/version.php
index e5212c652c..b0a5e13e2b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.5-alpha-36616';
+$wp_version = '4.5-alpha-36617';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-login.php b/wp-login.php
index 28dbaaed4b..64852134da 100644
--- a/wp-login.php
+++ b/wp-login.php
@@ -529,7 +529,7 @@ case 'retrievepassword' :
 
 <form name="lostpasswordform" id="lostpasswordform" action="<?php echo esc_url( network_site_url( 'wp-login.php?action=lostpassword', 'login_post' ) ); ?>" method="post">
 	<p>
-		<label for="user_login" ><?php _e('Username or Email:') ?><br />
+		<label for="user_login" ><?php _e('Username or Email') ?><br />
 		<input type="text" name="user_login" id="user_login" class="input" value="<?php echo esc_attr($user_login); ?>" size="20" /></label>
 	</p>
 	<?php
@@ -756,7 +756,13 @@ default:
 	// If the user wants ssl but the session is not ssl, force a secure cookie.
 	if ( !empty($_POST['log']) && !force_ssl_admin() ) {
 		$user_name = sanitize_user($_POST['log']);
-		if ( $user = get_user_by('login', $user_name) ) {
+		$user = get_user_by( 'login', $user_name );
+
+		if ( ! $user && strpos( $user_name, '@' ) ) {
+			$user = get_user_by( 'email', $user_name );
+		}
+
+		if ( $user ) {
 			if ( get_user_option('use_ssl', $user->ID) ) {
 				$secure_cookie = true;
 				force_ssl_admin(true);
@@ -882,7 +888,7 @@ default:
 
 <form name="loginform" id="loginform" action="<?php echo esc_url( site_url( 'wp-login.php', 'login_post' ) ); ?>" method="post">
 	<p>
-		<label for="user_login"><?php _e('Username') ?><br />
+		<label for="user_login"><?php _e('Username or Email') ?><br />
 		<input type="text" name="log" id="user_login"<?php echo $aria_describedby_error; ?> class="input" value="<?php echo esc_attr( $user_login ); ?>" size="20" /></label>
 	</p>
 	<p>