Originally founded as an independent developer in 1995, Ensemble Studios was a Microsoft-owned developer from 2001 to 2009, when it was officially disbanded. Ensemble has developed many games including the Age of Empires game series and Halo Wars. In addition to game development, Ensemble Studios also made the Genie Game Engine used in Age of Empires, Age of Empires II: The Age of Kings, and Star Wars: Galactic Battlegrounds.

Ensemble Studios developed the Age of Empires game series of real-time strategy titles, comprising Age of Empires, Age of Empires II: The Age of Kings and Age of Empires III. They also released Age of Mythology, a spin-off from the original series. Expansion packs were also released for all their games including two for Age of Empires III. Their last release was the real-time strategy game called Halo Wars for Xbox 360.

Ensemble released Age of Empires III, on October 18, 2005, in North America. The game follows from the end of Age of Empires II, set in times such as the Industrial Age. The lead-up to the game's announcement was a series of teasers on Ensemble's website, culminating in a number of in-game screenshots. The game has sold over 2 million copies, as of October 2007,[citation needed] and has become the fastest selling game of the series. Afterward, development began on the first expansion pack to Age of Empires III titled Age of Empires III: The War Chiefs. It included new content, new gameplay elements, a new single-player campaign, and three new native American civilizations. It was originally set for an October 2, 2006 release, but was released later, on October 17, 2006. On October 23, 2007, Ensemble released a second, and final expansion to Age of Empires III titled Age of Empires III: The Asian Dynasties. It introduced three Asian civilizations and six minor natives, as well as new gameplay features. They developed this project in conjunction with Big Huge Games, the creators of Rise of Nations. Ensemble also developed Halo Wars, a real-time strategy game for the Xbox 360 based on the successful Halo franchise. It was released on February 27, 2009 and sold one million copies in less than a month.

On September 9, 2008, it was announced that Ensemble will be closing after the release of Halo Wars. According to multiple independent reports, all non-essential staff have been laid off and remaining staff have been given incentives to remain until the completion of the project. Microsoft issued an internal statement on September 10, 2008 which was then leaked to the public. As reported on the Ensemble Studio blog in late 2008, the company shut down on January 29, 2009. It was also stated that there are at least two new studios being formed by ES employees. In February 2009 former Ensemble Studios head Tony Goodman started a new independent studio, Robot Entertainment, and a number of the existing employees have been offered a position in this company.Following the announcement of Robot Entertainment, former Ensemble Studios producer David Rippy started a new independent studio, Bonfire Studios, comprised entirely of former Ensemble staff members.[15] In March 2009, a third studio, Windstorm Studios was announced, founded by ex-staffer Dusty Monk. In May 2009, a fourth studio called Newtoy was created by several developers from Ensemble. Newtoy is already working on its first game for the iPhone.