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 corresponding to previous games in the series, all battles are real time, and enemies are no longer randomly encountered.

There are 32 public game worlds, a cluster of servers, available for play with approximately 15 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 who can send items between each other. 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.