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A Login and to log in (sometimes log on, or in IBM parlance , Signon and to sign on) refer to the process of accessing a computer by identification of the user in order to obtain credentials to permit access. It is an integral part of computer security procedure.

Growing out of the use of the term to clock in on arrival at a factory, where a worker would stamp a timesheet or card upon their arrival, to log in to a computer system is to identify yourself to the system. The use of a computer login procedure provides an audit trail of the use of the system in a similar manner.

To log in to a system usually requires

• a username; used in preference to the full name of the user this is a shorter sequence of characters which still uniquely identifies the person
• a password; another sequence of characters which provides the user with a key to the system and is kept secret from other users,

and optionally a further identifier indiciating the system, network or domain the user desires to access.

The group of identifiers is usually referred to as a login and the process of entering them to a system as to log in or log on.

The process creates a session on the target machine for the user, with limitations on what actions the user may perform set by the system software during the login process.

In the case of accessing an Internet website the site will often place cookies on the user's computer, which may either last just for the session or may be used on a later visit to the site.

When a user finishes their session they will Logout (or in IBM parlance, sign off).