Note: to create a user account for Wikipedia, go to the login page.

For other uses of the term UID, see the UID disambiguation article.

A user name (also called login name or logon) is a unique name for each user of computer services which can be accessed by several persons.

Users need to identify themselves for accounting, security, logging, and resource management. Usually a person must also enter a password in order to access a service. Once the user has logged on the operating system will often use an identifier, e.g. an integer, to refer to them rather than their user name.

User names are usually based on a short string of alphanumeric characters. Depending on the policies of the particular service, the name may be chosen by the user or assigned by a system administrator. Common choices are first name, initials, or some combination of first name, last name, initials and an arbitrary number. Sometimes the system dictates certain aspects in the choice of username. For example, the software requirements of wikis that use CamelCase mean that a user name on those wikis must have two capitalized words joined without spaces (e.g. UserName; this is sometimes called a WikiName). For security reasons, some systems require that a user name contain non-alphabet characters such as numbers or symbols, although this requirement is more commonly associated with passwords.

Computer security is usually tied to user management: a particular user (called Administrator or root) is given complete access to the system, while normal users have limitations on what they can do. Sometimes "users" are created for particular computer programs that need to access important features in their normal functioning or, in the opposite case, for programs that are likely to cause problems and must have as restricted access as possible to the system (the latter is the case for web servers, that are often by malicious users as a way to access the system).

User names are often also used as mailbox names in electronic mail addresses.