Xbox Game Studios, previously known as Microsoft Studios, Microsoft Game Studios, and Microsoft Games, is a division of Microsoft 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, Windows Mobile and other mobile platforms, and web-based portals. As the studio grew, it has acquired and relinquished ownership of several other studios, and is the parent organization of fifteen other studios.
Source: Wikipedia, "Xbox Game Studios", available under the CC-BY-SA License.