Many massively multiplayer online games (MMOs) are made with three-dimensional (3D) graphics. They cover nearly every genre of game, from science fiction to fantasy to historical simulations. Within those genres, 3D MMOs can be first-person shooters, role-playing games, social environments with no strict game logic, or more unique types such as puzzle games or real-time strategy games. The 3D graphics are sometimes used to enhance game play, as is the case with a first-person shooter, or to inspire an atmosphere, as can be done with elaborate role-playing game worlds. Some 3D MMOs can be match-based games in which players compete to defeat one another; sandbox, in which players determine how the game is played within a given rule set; or more guided games in which players walk through a narrative or other pre-made content in a specific order.
Visually, the genre of many 3D MMOs determines their visual style and the type of 3D graphics that are used. Science fiction games that take place in space tend to use more ephemeral special effects for astronomical bodies, while sword and sorcery fantasy games focus on character models and sharp object details. By far, most 3D MMOs are in the sword and sorcery fantasy genre, although espionage, sports and historical games also exist.
The type of game play in 3D MMOs can vary. Most first-person shooter games are defined by a player interface that requires good reflexes and response times to play; this often is known as a twitch game, because the short, rapid movements of the player's fingers on a keyboard while playing sometimes seem like twitching. The processor power and network bandwidth required for massively multiplayer twitch games that track every small player movement means that many such MMOs match players into smaller, more technically manageable groups for play inside a larger world.
A very broad category of 3D MMOs are role-playing games. Despite the connotations of role playing outside of MMOs, these games generally are defined by high levels of character customization, either during character creation or during character advancement. Unlike twitch games, most role-playing games use a point-and-click interface so characters in the game move predictably across the 3D terrain, reducing the need for the servers to track every small movement. This allows role-playing games to have large worlds in which thousands of players are able to interact persistently at the same time. Role-playing MMOs also make good use of 3D graphics to build large, fantastical worlds that can, on occasion, push the limits of what 3D graphics cards can display.
Social 3D MMOs provide players with a world they can use as a blank canvas. Several games give players the ability to build 3D environments to show off to other players, while a different type of social game is more like a chat room with 3D avatars. Some unique types of 3D MMOs have emerged through a fusion of social games and other genres, creating games in which social interaction can translate into in-game virtual character advancement.