The Matrix Online (abbreviated as MxO) is a discontinued massively multiplayer online role-playing game (MMORPG) initially developed by Monolith Productions and later, a few months after launch, by Sony Online Entertainment. It was advertised as a continuation of the storyline of The Matrix films, as The Wachowskis, the franchise's creators, gave their blessing to the notion of gamers "inherit[ing] the 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 released MxO on March 22, 2005, in the United States. It was released in Europe on April 15, 2005. In June, Warner Bros. sold the rights to the game to Sony Online Entertainment, and the game's development and operation was transferred to the latter on August 15, 2005. Sony Online Entertainment shut down operation of the game on July 31, 2009.

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 second and third The Matrix films and an overcrowded MMORPG market.

In The Matrix Online, the player assumes the role of a redpill, a human who was formerly trapped inside the Matrix and has since been freed and shown the truth of humanity's imprisonment. 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 mind from the Matrix and allow them to take the body of a physical human and experience reality. 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 large metropolis that the entire Matrix story is set in).

Combat in the game is divided into two separate parts: Free-fire and Interlock. Free-fire mode allows for large gun battles to take place, while Interlock is often broken down into bullet-time-affected martial arts moves and close-quarters gunfire.

There are three main classes in The Matrix Online: Coder, Hacker, and Operative. Coders create a special "simulacrum" that fights for them. Hackers manipulate the code of the Matrix to affect friends and enemies from a distance, either damaging them, downgrading their combat abilities, or healing them and upgrading their powers. Operatives are the common soldiers seen from the movies - Martial Artists, Gunmen, and the new Spy class, which revolves around stealth fighting and knife throwing. Magazines never seem to run out of bullets and knife throwers also have an unlimited supply.

In free-fire mode, operatives exchange damage with each other. Gunmen and Hackers are well-equipped for this, with their ranged attacks and abilities. Martial Artists must get close to their targets to be effective, and although a Spy's most dangerous abilities are initiated out of Interlock, they also pull their opponents into Interlock. Each attack or ability is used at timed intervals, based on the system of damage per second (D.P.S.). For example, the strongest rifle in the Matrix does 15 damage points per second and has a fire rate of 3.5 seconds, which, in free-fire, causes the rifle to have a base damage of 52.5, to be altered by the player's own stats. Opposed to such, a Hacker's stronger attack ability such as Logic Barrage 4.0 does 63 D.P.S., but with a short casting timer, does base damage of only 120-180 damage.

In Interlock or Close Combat, two players exchange damage in rounds. Each round lasts exactly four seconds. For each round, the two players' accuracies are pitted against each other's defenses, which are slightly affected by a random "luck" roll. There are three different outcomes to a round: hit-hit, hit-miss, or miss-miss. In hit-miss, one of the players will hit the other while dodging or blocking their attack. In miss-miss, both players will parry each other without doing damage. In hit-hit, one player will damage the other, only to be damaged themselves in a counterattack. When special abilities are used, however, there can be no hit-hit round, although the miss-miss round can still apply.

When taking or dealing damage, one player's damage influences are pitted against another player's resistance influences of the same damage type (i.e. a gunman's ballistic damage versus an opponent's ballistic resistance). Higher resistance versus lower damage means that the defending player will not take as much damage.