The Matrix Online (also known as MxO) is a massively multiplayer online game developed by Monolith Productions. It is an official continuation of the The Matrix storyline. The game began closed beta-testing in June 2004 which was then opened for people who pre-ordered the game in November 2004. Warner Bros. and Sega officially released MxO on 22 March 2005 in the United States. It was released in Europe on April 15, 2005. Ubisoft backed out of an agreement to co-publish the game, not long after canceling plans for another MMORPG. Ubisoft and Warner Bros. stated that this did not have a negative impact on their relationship. At the time, doubts about the game circled within the industry, based on the lackluster reception of the later two Matrix films and an overcrowded MMORPG market.

On 17 June 2005, Warner Bros. and Sony Online Entertainment, owners of several other online multiplayer game worlds, including EverQuest and Star Wars Galaxies, announced that SOE had picked up the rights from Monolith to operate The Matrix Online. The transition to SOE was completed on 15 August 2005. On 29 May 2009, Sony announced that the Matrix Online would be unplugged on July 31, 2009.

The player assume the role of a redpill, a human who was formerly trapped inside the Matrix. When creating a new character, the player is given the choice of taking a blue pill that will return them to their former life (quit the game) or a red pill, which will free their minds from the Matrix. Characters who are unaware of the fact that they are in the simulation are often referred to as "bluepills" because they have either taken the blue pill or have not been given the choice yet. People who are aware of the simulation (players) are referred to as "redpills" because they have taken the red pill (or, in very rare cases, when a character has self-substantiated out of the Matrix on their own). Following the choice between the two pills, the player is then taken through a basic tutorial of the game`s mechanics, including mission interaction and the combat system. After the tutorial, they are then free to roam the Mega City (the city that the entire Matrix story is set in).

The Matrix Online has a unique class system. Players can load abilities they have either purchased or produced (by the Coder class, known ingame as coding) at Hardlines, provided they have enough memory and the abilities that precede the loading one. These abilities can then be switched out at a Hardline at a moment`s notice. This leads to a very flexible class system, without players being stuck in one class. The three main archetypes are Hacker, Coder, and Operative. They are similar to the classes Mage, Crafter, and Fighter in other MMORPGs. These classes then each branch out into sub-classes, with Coder, for example being divided into Programmer (out of battle item and ability maker) and Code Shaper (creates simulacrums to fight with, similarities to a necromancer/summoner in other MMOs). To elaborate, the game currently has a total of 21 end-game classes with an additional two stubs.

Another of The Matrix Online`s defining and differentiating aspects is its inclusion and emphasis on what is called "The Continuing Story". This is to say the game itself is the official continuation of the universe, story and characters established in The Matrix series of fictional works including the Movie Trilogy, the Animatrix short films, the "Enter The Matrix" video game and a series of officially written and produced Matrix comic books. This continuation is written collaboratively between the award winning comic book writer Paul Chadwick and MxO lead game designer, Ben "Rarebit" Chamberlain. It has also been confirmed as having seen verification and input from "Matrix" creators, The Wachowski Brothers, through the end of Chapter 9. As of March 21, 2008, a Producer Letter by Daniel "Walrus" Myers has recently announced that Paul Chadwick is leaving The Matrix Online for other projects and that the storytelling format would change by utilizing the neglected in-game newspaper The Sentinel, with the Live Events Special Interest Group working on the paper while removing the cinematics.