|This page in a nutshell: When choosing an account name, do not choose names which may be offensive, misleading, disruptive, or promotional. The username should represent one person; do not use your organisation's name.|
|To report blatant violations of the username policy, visit Wikipedia:Usernames for administrator attention (WP:UAA).|
This policy describes what kinds of usernames are acceptable on the English Wikipedia and how unacceptable or doubtful usernames can be dealt with. It also specifies that a user account should be used only by one person, and that in most cases one person should use only one account.
You choose your username when creating a user account. All contributions made using that account will then be attributed to the chosen username (contributions made while not logged in to any account are attributed to the user's IP address). It is also possible to request a change of username, and have your past contributions re-attributed to the new name.
This policy applies to usernames on English Wikipedia. However, in most cases you will be able to use the same username and password to log in to other language Wikipedias and other Wikimedia Foundation supported projects. See Wikipedia:Unified login.