A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure.

Valve Corporation (also known as Valve Software or simply as Valve, and stylized as VALV^E) is an American video game development and digital distribution company based in Bellevue, Washington, United States. Founded in 1996 by former Microsoft employees Gabe Newell and Mike Harrington, Valve became famous from its critically acclaimed Half-Life series, (the first game 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 Valve game since its introduction in 2004.