MMORPG stands for massively multiplayer online role playing game, a type of MMOG (massively multiplayer online game). An MMORPG is a computer-based RPG (role playing game) which takes place in an online virtual world with hundreds or thousands of other players. In an MMORPG, a player uses a client to connect to a server, usually run by the publisher of the game, which hosts the virtual world and memorizes information about the player.

In an MMORPG, like any RPG, the user controls a character represented by an avatar, which he directs to fight monsters for experience, interact with other characters, acquire items, and so on. MMORPGs have become extremely popular since the wider debut of broadband Internet connections, now with millions of subscribers from hundreds of different countries. Some MMORPGs have as many as a million subscribers.

MMORPGs have their roots in online, text-based adventures, which existed as early as the 1970s. The first real MMORPG, Meridian 59, was released in 1996, but it wasn't until the next year that Ultima Online highly popularized the genre. Both games were played on a pay-by-month basis, as are most modern MMORPGs. The genre surged into popularity throughout the late nineties, finding especially welcoming markets in Taiwan, South Korea, and America. In 1999, Sony Online Entertainment released EverQuest, a popular game to this day. Right around the same time, Ultima Online and Asheron's Call were released, two other MMORPGs that would become extremely popular.

In 2001, the market appeared to plateau, causing the cancellation of some MMORPGs in development. But new MMORPGs continue to be released, with dozens of popular games still being sold. One popular selling point is expansion packs, either downloaded from the server as patches or sold in stores. These expansion packs ensure that the virtual worlds in MMORPGs stay fresh and interesting, constantly changing.

Around 2000, MMORPGs began to attract the attention of academia (psychology and economics) and non-gaming publications. Reactions ranging from praise to distaste are common, with some critics saying that such games turn us into lifeless zombies, and others celebrating the MMORPG as a fascinating new way for us to interact with each other.

Some MMORPGs have developed sophisticated economies with equipment, currency, and characters within the game being exchanged online for real money. This has led to the study of "synthetic economies" and how they relate to real world economies. As MMORPG worlds become increasingly more realistic and entertaining, they will continue to permeate further into the mainstream, attracting both positive and negative reactions from all sides.