In computer security, logging in, (or logging on or signing in or signing on), is the process by which an individual gains access to a computer system by identifying and authenticating themselves. The user credentials are typically some form of "username" and a matching "password", and these credentials themselves are sometimes referred to as a login, (or a logon or a sign in or a sign on). In practice, modern secure systems also often require a  second factor for extra security.

;lo gin: is a long-running bi-monthly technical journal published by the USENIX Association, focusing on the UNIX operating system and system administration in general. It was founded by Mel Ferentz in 1975 as UNIX News, changing its name to ;login: in 1977.