Halo 2 is a science fiction first-person shooter video game developed by Bungie Studios. Released for the Xbox game console on November 9, 2004, the game is the sequel to Halo: Combat Evolved. After its initial release, Halo 2 was the most popular video game on Xbox Live, holding that rank until the release of Gears of War for the Xbox 360 nearly two years later. By June 20, 2006, more than 500 million games of Halo 2 had been played and more than 710 million hours have been spent playing it on Xbox Live; by May 9, 2007, this number had risen to more than five million unique players on Xbox Live. As of May 9, 2006, Halo 2 is the best-selling first-generation Xbox game with 8 million copies sold worldwide. As of September 25 2007, Halo 2 is the fifth best-selling video game in the United States with 6.3 million copies sold in the US alone. The game features a new game engine, as well as using the Havok physics engine; added weapons and vehicles; new multi-player maps; and a continuation of the storyline from Halo: Combat Evolved. In the game, humans, who have developed faster-than-light travel and colonized hundreds of worlds, have been engaged in a war against a collective of genocidal alien races, the Covenant. The player assumes the roles of Master Chief and the Arbiter, and fights enemies on foot or with a collection of alien and human vehicles. Critical reception of the game was generally positive, with most publications lauding the strong multiplayer component; at the same time, the campaign was the focus of criticism for its cliffhanger ending.

A Windows Vista version of the game was released on May 17, 2007. It was developed by a team at Microsoft Game Studios who are referred to internally as "Hired Gun". Game developer Pi Studios produced editing tools for this version, which allows users to create multiplayer maps.