Valve Corporation (formerly Valve Software, commonly referred to as Valve) is an American video game development and digital distribution company headquartered in Bellevue, Washington, United States. Its European-based office opened in 2012 in Luxembourg. Founded in 1996 by former Microsoft employees Gabe Newell and Mike Harrington, Valve developed critically acclaimed video game series Half-Life, Portal, and Left 4 Dead. It has also developed and maintains the Source engine for which most of its games run on, and the software distribution platform Steam, which has led to the Steam Machine, a line of pre-built gaming computers running SteamOS. More: en.wikipedia.org.