Final Fantasy XI, also known as Final Fantasy XI Online, is a massively multiplayer online role-playing game (MMORPG) developed and published by Square (later Square Enix) as part of the Final Fantasy series. It was released in Japan on Sony`s PlayStation 2 on May 16, 2002, and was released for Microsoft`s Windows-based personal computers in November 2002. The PC version was released in North America on October 28, 2003, and the PlayStation 2 version on March 23, 2004. In Europe, only the Windows version was released, on September 17, 2004. An Xbox 360 version was released worldwide in April 2006 for all regions, as the system`s first MMORPG and the first cross-platform MMORPG. The Xbox 360 version does not require an Xbox Live Gold account, but as is the norm for MMORPGs, all versions require a monthly subscription to the game.

The story is set in the fantasy world of Vana`diel, where tasks can be performed to improve a character`s powers or to complete quests. Players are able to customize a character that they will guide through the story. There are also thousands of quests that allow players to gain various rewards, as well as a growing number of player versus player competitions.

In April 2009, Square Enix announced that the total number of active characters exceeded 2 million for the first time in game history. Previously Square Enix had announced that more than 500,000 users, using more than one million characters, were playing the game as of January 2004. As of 2006, between 200,000 and 300,000 active players logged in per day, and the game remains the dominant MMORPG in Japan. As of 2008, in an announcement for three additional expansions in development, SE noted Final Fantasy XI still has a strong user base of around 500,000 subscribers. As of April 22nd, 2009 there are 2,000,000 active players. Four expansions for the game have been released, capitalizing on the game`s success.

Final Fantasy XI, in addition to being an MMORPG, differs from previous titles in the series in several ways. Unlike the predefined main characters of previous Final Fantasy titles, players are able to customize their characters in limited ways, including race, gender, face, hair color, body size, job, and allegiance. Also diverging from previous games in the series, all battles are real time, and enemies are no longer randomly encountered, a trend continued in FFXII. There are 32 public game worlds, a cluster of servers, available for play with approximately 15,000 to 20,000 players in each. The servers are named after summoned monsters from previous Final Fantasy titles, such as Ifrit and Diabolos. Players have the ability to move between servers, though few do; more common is the creation of different characters on different servers. There are no region-specific or system-specific servers, and unlike most online games, players of different languages play in the same world and can interact through automatic language translation from a library of translated phrases. The game servers are run by Square-Enix as part of their PlayOnline network.

Players have the option of using any combination of a keyboard, mouse, and controller to play Final Fantasy XI. If a player using a PlayStation 2 or an Xbox 360 does not have a keyboard, the game provides a method for communication within the game. The heads-up display in Final Fantasy XI consists of a log window, menus, and several game information elements. The log window at the bottom of the screen displays system messages, battle messages, and text input by other players. Players may choose to filter what appears in the log window.