Anonymous File Transfer Protocol allows the public to log into an FTP server with a common login (usually "ftp" or "anonymous" and any password (usually the person's e-mail address is used as the password). Anonymous FTP is benefitial for the distribution of large files to the public, avoiding the need to assign large numbers of login and password combinations for FTP access.

After login to an anonymous FTP server a user has access to a special directory hierarchy containing the publically accessible files, typically in a subdirectory called "pub". This is usually a separate area from files used by local users.

A reference like ftp://some.server.com/pub/dir1/infomeans that files are available by anonymous FTP from the host called some.server.com in the directory (or file) /pub/dir1/info. Sometimes the hostname will be followed by an Internet address in parentheses. The directory will usually be given as a path relative to the anonymous FTP login directory. A reference to a file available by FTP may also be in the form of a URL starting "ftp:".

Many FTP sites are protected. Unlike anonymous FTP sites, these restricted FTP sites can only be accessed by individuals who enter a valid username and password.