Counter-Strike (officially abbreviated as CS) is a series of multiplayer first-person shooter video games, in which teams of terrorists and counter-terrorists battle to, respectively, perpetrate an act of terror (bombing, hostage-taking) and prevent it (bomb defusal, hostage rescue). The series began on Windows in 1999 with the first version of Counter-Strike. It was initially released as a modification for Half-Life and designed by Minh "Gooseman" Le and Jess "Cliffe" Cliffe, before the rights to the game's intellectual property were acquired by Valve Corporation, the developers of Half-Life.
The game was followed-up with Counter-Strike: Condition Zero, developed by Turtle Rock Studios and released in 2004.
Later that same year, Counter-Strike: Source was released by Valve. Released only eight months after Counter-Strike: Condition Zero, in November 2004, the game was a remake of the original Counter-Strike and the first in the series to run on Valve's newly created Source engine.
The fourth game in the main series to have been developed by Valve, Counter-Strike: Global Offensive, was released in 2012 for Windows, OS X, Xbox 360, and PlayStation 3. Hidden Path Entertainment, who also worked on Counter-Strike: Source post-release, helped to develop the game alongside Valve. There have been several community made "spin off" titles created over the years.