Gears of War is a 2006 third-person shooter video game developed by Epic Games and published by Microsoft Game Studios. It is the first installment of the Gears of War series, and was initially released as an exclusive title for the Xbox 360 in November 2006. A Microsoft Windows version, developed in conjunction with People Can Fly, was released in November 2007. The game's main story, which can be played in single or co-operative play, focuses on a squad of troops who assist in completing a desperate, last-ditch attempt to end a war against a genocidal subterranean enemy, the Locust, and save the remaining human inhabitants of their planet Sera. The game's multiplayer mode allows up to eight players to control characters from one of the two factions in a variety of online game modes. Gameplay features players using cover and strategic fire in order to win battles.

The game was a commercial success, selling over three million copies within ten weeks of its launch. It became the fastest selling video game of 2006, the second-most played game over Xbox Live during 2007, and one of the best-selling Xbox 360 games. The game received universal acclaim for its gameplay and detailed visuals, and is considered to be one of the greatest video games ever made, winning over 30 "Game of the Year" awards in 2006. A remastered version, Gears of War: Ultimate Edition, was developed primarily by The Coalition. Ultimate Edition was released for the Xbox One in August 2015, and for Microsoft Windows in March 2016.

Gears of War's success led to the development of a franchise, including four sequels: Gears of War 2 (2008), Gears of War 3 (2011), Gears of War 4 (2016), and Gears 5 (2019), and two prequels, Gears of War: Judgment (2013) and Gears Tactics (2020). In addition, it has also spawned adaptations for books and comics, and a film based on the series is currently in development.