Xbox Game Studios (previously known as Microsoft Studios, Microsoft Game Studios, and Microsoft Games) is an American video game publisher based in Redmond, Washington. It was established in March 2000, spun out from an internal Games Group, for the development and publishing of video games for Microsoft Windows. It has since expanded to include games and other interactive entertainment for the namesake Xbox platforms, other desktop operating systems, Windows Mobile and other mobile platforms, web-based portals, and other game consoles.

Xbox Game Studios, alongside ZeniMax Media and Activision Blizzard, are part of the Microsoft Gaming division led by Phil Spencer, who is chief executive officer of the division.

In the early 1990s, Microsoft published a few video games. It published subLOGIC's Microsoft Flight Simulator and several Microsoft Entertainment Pack compilations of minigames, but was best known for MS-DOS and Microsoft Windows. In 1992, the company began increasing its focus on games. It announced Microsoft Golf for Windows, based on Access Software's Links, and expanded the games division from two to six people with the intention of commissioning more products from other developers.

Microsoft acquired FASA Interactive in 1999 for its MechWarrior game series, Access Software, and Aces Game Studio, which worked on Flight Simulator. The Games Group had also established long-term publishing deals with developers like Ensemble Studios (Age of Empires, Age of Mythology), and Digital Anvil (Starlancer). Under Microsoft, FASA Interactive was renamed FASA Studio, and Access Software became Salt Lake Games Studio.

Microsoft transitioned the Games Group into a wholly separate division named Microsoft Games around March 2000, along with other consolidation of games-related projects within Microsoft. This came alongside the public announcement of the first Xbox console, with Microsoft Games to serve as a developer and publisher of titles for both Xbox and Windows. Robbie Bach, who held executive positions in Microsoft's entertainment divisions, was named senior vice-president while Ed Fries, a member of the former Games Group and instrumental for some of its acquisitions, was named as vice-president of the new division. Shane Kim served as the division's general manager. In 2001, the division was renamed Microsoft Game Studios (MGS).

FASA Studio and Salt Lake Games Studio remained with Microsoft Game Studios. Digital Anvil and Ensemble Studios were acquired by Microsoft in 2000 and 2001, respectively. One of the first major studio acquisitions following the division's formation was Bungie in June 2000, in the midst of its development of Halo: Combat Evolved. With the acquisition, Halo, which had been planned for release on personal computers, became a Microsoft-published title as well as a launch title for the Xbox on its release in 2001. Turn 10 Studios was established in 2001 for work on the Forza series of racing games. In September 2002, Microsoft Game Studios acquired Rare, who had previously extensively developed for Nintendo platforms. In 2003, Microsoft recognized that the EA Sports label was in a far stronger position to develop sports games for the Xbox console, and among realignment steps, laid off about 78 employees within Microsoft Game Studios that were developing sports games in-house, and sold Salt Lake Games Studio, now named Indie Games to Take-Two Interactive in 2004, where it became Indie Built.

Peter Moore was named in 2003 as vice-president of Microsoft's Home and Entertainment Division, which included MGS, the Xbox division, and Microsoft's home hardware market, reporting to Bach. In addition to pulling big publishers like Electronic Arts to the Xbox platform, Moore tried to push the Xbox in Japan by courting Japanese developers with support from MGS publishing. Such games included Phantom Dust and Blinx: The Time Sweeper. Around 2004, MGS established Carbonated Games as an internal studio for the development of casual games for Microsoft's web games portal MSN Games, on the chat client MSN Messenger, and on the Xbox Live platform. Kim and Fries were instrumental for securing MGS' publishing deal with Lionhead Studios for their 2004 game Fable, which would serve as the first major role-playing game on the Xbox platform. Subsequently, in 2006, MGS acquired Lionhead Studios along with the Fable properties, as it sought to secure a Fable sequel for the upcoming Xbox 360. MGS folded the staff of Digital Anvil into the larger studio in 2005, following the release of 2003's Brute Force, and closed down the studio entirely in 2006. FASA Studio was closed three-and-a-half months after the May 2007 release of their last game, Shadowrun.

In 2007, MGS announced the opening of a European office in Reading, England, headed by general manager Phil Spencer. Moore opted to leave Microsoft in July 2007, so to move back to the San Francisco Bay area with his family and to rejoin Electronic Arts. Don Mattrick was named as his replacement as the new vice-president of the Xbox and Games Business, which included MGS. Later in 2007, Bungie amicably split from MGS to become a privately held independent company, with MGS retaining the rights to the Halo property. Bungie continued to develop two additional Halo games for MGS, Halo 3: ODST (2009) and Halo: Reach (2010). Simultaneously, MGS founded 343 Industries as an internal studio to develop future Halo games without Bungie.