Microsoft Flight Simulator X (abbreviated as FSX) is a 2006 flight simulation video game originally developed by Aces Game Studio and published by Microsoft Game Studios for Microsoft Windows. It is the sequel to Microsoft Flight Simulator 2004 and the tenth and most current installment of the Microsoft Flight Simulator series, which was first released in 1982. It is built on an upgraded graphics rendering engine, showcasing DirectX 10 features in Windows Vista and was marketed by Microsoft as the most important technological milestone in the series to date. FSX is the first version in the series to be released on DVD media.

In December 2012, over six years after its release, the FSX multiplayer matchmaking system over the GameSpy network was discontinued. On July 9, 2014, Dovetail Games, the developer of Train Simulator, announced that it signed a licensing agreement with Microsoft to continue development on FSX and the production of new content.[2] On December 18, 2014, the FSX: Steam Edition version of the simulator was made available through digital distribution via Steam. The updated release of FSX includes support for Windows 8.1 and later, along with updated hosting of FSX multiplayer features through Steam.