Halo 3 is a first-person shooter video game developed by Bungie Studios exclusively for the Xbox 360. The game is the third title in the Halo series and ends the story arc begun in Halo: Combat Evolved and continued with Halo 2. The game was released on September 25, 2007 in New Zealand (which due to its midnight release made it first available for official retail), Australia, Singapore, India, Mexico, Canada, Brazil, and the United States; September 26, 2007 in Europe; and September 27, 2007 in Japan. GameSpot reported that 4.2 million units of Halo 3 were in retail outlets on September 24, 2007, a day before official release, a world record volume release. Halo 3 also holds the record for the highest grossing opening day in video game history, making US$170 million in its first 24 hours. On October 4, 2007, Reuters UK estimated that Halo 3 may have sold up to 5.2 million copies.

The game features new vehicles, weapons, and gameplay features not present in the previous titles of the series. Halo 3 focuses on the interstellar war between 26th century humanity and a collection of alien races known as the Covenant, who after a decades-long war have begun the invasion of Earth. The player assumes the role of the Master Chief, a cybernetically enhanced supersoldier, as he wages war in defense of humanity.