Halo: Combat Evolved is a 2001 first-person shooter video game developed by Bungie and published by Microsoft Game Studios. The game was released on November 15, 2001 for the Xbox, with a Microsoft Windows and Mac OS X port released in 2003, and a downloadable Xbox 360 port released in 2007 as part of Xbox Originals. It is the first installment in the Halo franchise. Set in the 26th century, players assume the role of Master Chief, a cybernetically enhanced supersoldier. Accompanied by an artificial intelligence construct named Cortana and the forces of the United Nations Space Command (UNSC), players battle against an alien theocracy known as the Covenant while they attempt to uncover the secrets of the eponymous Halo, a ring-shaped artificial world.

Bungie began the development of what would eventually become Halo in 1997. Initially, the game was a real-time strategy game that morphed into a third-person shooter before becoming a first-person shooter. During development, Microsoft acquired Bungie and turned Halo into a launch game for its first video game console, the Xbox. Halo was a critical and commercial success and is often cited as one of the greatest video games ever made. Particular acclaim was given for its campaign, graphics, soundtrack, and multiplayer, although minor criticism focused on the campaign's level design.

More than six million copies were sold worldwide by November 2005, making it the second best-selling Xbox game and spawning a multimedia franchise. A sequel, Halo 2, was released for the Xbox in 2004. A remaster of the game, Halo: Combat Evolved Anniversary, was released for Xbox 360 by 343 Industries in 2011, the 10th anniversary of the original game's launch, and was re-released alongside the original competitive multiplayer as part of Halo: The Master Chief Collection in 2014. A remake, Halo: Campaign Evolved, is set for release on PlayStation 5, Windows, and Xbox Series X/S in 2026.