diff --git a/wp-includes/registration.php b/wp-includes/registration.php
index 041e8fc2c7..48fb2b1c8f 100644
--- a/wp-includes/registration.php
+++ b/wp-includes/registration.php
@@ -1,9 +1,17 @@
 <?php
+/**
+ * User Registration API
+ *
+ * @package WordPress
+ */
 
 /**
- * Checks whether the given username exists.
+ * username_exists() - Checks whether the given username exists.
+ *
+ * @since 2.0.0
+ *
  * @param string $username Username.
- * @return mixed The user's ID on success, and null on failure.
+ * @return null|int The user's ID on success, and null on failure.
  */
 function username_exists( $username ) {
 	if ( $user = get_userdatabylogin( $username ) ) {
@@ -14,10 +22,13 @@ function username_exists( $username ) {
 }
 
 /**
- * Checks whether the given email exists.
- * @global object $wpdb WordPress database layer.
+ * email_exists() - Checks whether the given email exists.
+ *
+ * @since 2.1.0
+ * @uses $wpdb
+ *
  * @param string $email Email.
- * @return mixed The user's ID on success, and false on failure.
+ * @return bool|int The user's ID on success, and false on failure.
  */
 function email_exists( $email ) {
 	if ( $user = get_user_by_email($email) )
@@ -27,9 +38,13 @@ function email_exists( $email ) {
 }
 
 /**
- * Checks whether an username is valid.
+ * validate_username() - Checks whether an username is valid.
+ *
+ * @since 2.0.1
+ * @uses apply_filters() Calls 'validate_username' hook on $valid check and $username as parameters
+ *
  * @param string $username Username.
- * @return bool A filtered boolean.
+ * @return bool Whether username given is valid
  */
 function validate_username( $username ) {
 	$sanitized = sanitize_user( $username, true );
@@ -38,8 +53,51 @@ function validate_username( $username ) {
 }
 
 /**
- * Insert an user into the database.
- * @global object $wpdb WordPress database layer.
+ * wp_insert_user() - Insert an user into the database.
+ *
+ * Can update a current user or insert a new user based on whether
+ * the user's ID is present.
+ *
+ * Can be used to update the user's info (see below), set the user's
+ * role, and set the user's preference on whether they want the rich
+ * editor on.
+ *
+ * Most of the $userdata array fields have filters associated with
+ * the values. The exceptions are 'rich_editing', 'role', 'jabber',
+ * 'aim', 'yim', 'user_registered', and 'ID'. The filters have the
+ * prefix 'pre_user_' followed by the field name. An example using
+ * 'description' would have the filter called, 'pre_user_description'
+ * that can be hooked into.
+ *
+ * The $userdata array can contain the following fields:
+ * 'ID' - An integer that will be used for updating an existing user.
+ * 'user_pass' - A string that contains the plain text password for the user.
+ * 'user_login' - A string that contains the user's username for logging in.
+ * 'user_nicename' - A string that contains a nicer looking name for the user.
+ *		The default is the user's username.
+ * 'user_url' - A string containing the user's URL for the user's web site.
+ * 'user_email' - A string containing the user's email address.
+ * 'display_name' - A string that will be shown on the site. Defaults to user's username.
+ *		It is likely that you will want to change this, for both appearance and security
+ *		through obscurity (that is if you don't use and delete the default 'admin' user).
+ * 'nickname' - The user's nickname, defaults to the user's username.
+ * 'first_name' - The user's first name.
+ * 'last_name' - The user's last name.
+ * 'description' - A string containing content about the user.
+ * 'rich_editing' - A string for whether to enable the rich editor or not. False if not
+ *		empty.
+ * 'user_registered' - The date the user registered. Format is 'Y-m-d H:i:s'.
+ * 'role' - A string used to set the user's role.
+ * 'jabber' - User's Jabber account.
+ * 'aim' - User's AOL IM account.
+ * 'yim' - User's Yahoo IM account.
+ *
+ * @since 2.0.0
+ * @uses $wpdb WordPress database layer.
+ * @uses apply_filters() Calls filters for most of the $userdata fields with the prefix 'pre_user'. See note above.
+ * @uses do_action() Calls 'profile_update' hook when updating giving the user's ID
+ * @uses do_action() Calls 'user_register' hook when creating a new user giving the user's ID
+ *
  * @param array $userdata An array of user data.
  * @return int The newly created user's ID.
  */
@@ -140,7 +198,21 @@ function wp_insert_user($userdata) {
 }
 
 /**
- * Update an user in the database.
+ * wp_update_user() - Update an user in the database
+ *
+ * It is possible to update a user's password by specifying the
+ * 'user_pass' value in the $userdata parameter array.
+ *
+ * If $userdata does not contain an 'ID' key, then a new user
+ * will be created and the new user's ID will be returned.
+ *
+ * If current user's password is being updated, then the cookies
+ * will be cleared.
+ *
+ * @since 2.0.0
+ * @see wp_insert_user() For what fields can be set in $userdata
+ * @uses wp_insert_user() Used to update existing user or add new one if user doesn't exist already
+ *
  * @param array $userdata An array of user data.
  * @return int The updated user's ID.
  */
@@ -176,9 +248,15 @@ function wp_update_user($userdata) {
 }
 
 /**
- * A simpler way of inserting an user into the database.
- * @see wp_insert_user().
- * @global object $wpdb WordPress database layer.
+ * wp_create_user() - A simpler way of inserting an user into the database.
+ *
+ * Creates a new user with just the username, password, and email. For a more
+ * detail creation of a user, use wp_insert_user() to specify more infomation.
+ *
+ * @since 2.0.0
+ * @see wp_insert_user() More complete way to create a new user
+ * @uses $wpdb Escapes $username and $email parameters
+ *
  * @param string $username The user's username.
  * @param string $password The user's password.
  * @param string $email The user's email (optional).