Valve Corporation (also known as Valve Software or simply Valve) is an American video game development and digital distribution company based in Bellevue, Washington, United States. It was founded in 1996 by former Microsoft employees Gabe Newell and Mike Harrington, and made famous by its highly successful and critically acclaimed first product, Half-Life, released in November 1998. It is also well known for its social-distribution network Steam, and for developing the Source engine, which has been used in every product since its introduction in 2004. - Source: Wikipedia