Halo 3 is a first-person shooter video game. It is based on the fictional events and settings in the Halo universe, and concludes the series. It was developed by Bungie Studios and published by Microsoft. Halo 3 was released on September 25, 2007 in Australia, Brazil, India, New Zealand, North America, and Singapore; September 26, 2007 in Europe; and September 27, 2007 in Japan all exclusively for the Xbox 360.

The game is rated "M" for Mature for blood, gore, violence, and mild language by the ESRB. Europe's PEGI rating system gave the game a "16+" rating, which serves as a guideline rather than as a rule. It is rated "15" by the BBFC for UK release and rated "M" by the OFLC for Australia and New Zealand release.

Upon its release, Halo 3 grossed US$300 million in its first week. More than one million people played Halo 3 on Xbox Live in the first twenty hours. As of January 3, 2008, Halo 3 has sold 8.1 million copies, and was the best-selling video game of 2007 in the U.S.. Overall, the game was very well-received by critics, with the Forge and multiplayer offerings singled out as strong features. By March 2009 more than 1 billion online matches had been played.