List of Steam titles

This is a list of video games available on Steam, a digital distribution service and online gaming community operated by Valve Corporation. Steam was launched in 2003, initially with Valve's own titles. The network gained more widespread use after the release of Half-Life 2 in 2004, which was intrinsically integrated into the system. Steam has since expanded as other major publishers, including Eidos Interactive, Activision, Ubisoft and Electronic Arts began distributing a number of their titles over the system. A substantial number of independent titles have also been released, along with several modifications for Valve's own games. As of May 2010, over 2427 titles are available over the service. A list of upcoming titles is also present on the service.

In early 2008, Valve began a program labeled Steamworks, offering client developers the opportunity to use Steam's distribution tools to their fullest extent in their products. Steamworks incorporates several additional features, such as achievements, Steam Community and matchmaking functions as well as Steam Cloud options.

Several titles make use of Microsoft's Games for Windows - LIVE system in addition to Steam. Those titles do not use Steam achievement system since Games for Windows - LIVE uses Microsoft's own gaming service, with its own achievement system (Gamerscore).

Modifications
In September 2008, Valve announced that the company would begin to host modifications based on the Source engine on the Steam system, available for download through the system. The developers of the modifications are then given the ability to deliver updates for their projects through Steam; other modifications are available, but cannot make use of this distribution service. In addition, the modifications can be augmented with Steamworks features such as achievements, improved Steam community functions and individual player statistics. Each modification is free to download, but requires the client Steam account to possess at least one Source game developed by Valve, such as Half-Life 2, Counter-Strike: Source or Team Fortress 2. As of February 2009, eight Source engine modifications and two modifications for Red Orchestra: Ostfront 41-45 are available through Steam.