Counter-Strike (commonly abbreviated to CS) is a tactical first-person shooter video game which originated from a Half-Life modification by Minh "Gooseman" Le and Jess "Cliffe" Cliffe. The game has been expanded into a series since its original release, which currently includes Counter-Strike: Condition Zero, Counter-Strike: Source, Counter-Strike: Anthology and Counter-Strike on Xbox. Counter-Strike pits a team of counter-terrorists against a team of terrorists in a series of rounds. Each round is won by either completing the mission objective or eliminating the opposing force. The latest incarnation of the game, Counter-Strike: Source, is based on the Source engine developed for Half-Life 2.