Counter-Strike is a first-person shooter video game developed by Valve Corporation. It was initially developed and released as a Half-Life modification by Minh "Gooseman" Le and Jess "Cliffe" Cliffe in 1999, before Le and Cliffe were hired and the game's intellectual property acquired. Counter-Strike was first released by Valve on the Microsoft Windows platform in 2000. The game later spawned a franchise, and is the first installment in the Counter-Strike series.

A player can choose to play as one of eight different default character models (four for each side, although Counter-Strike: Condition Zero added two extra models, bringing the total to ten). Players are generally given a few seconds before the round begins (known as "freeze time") to prepare and buy equipment, during which they cannot attack or move. They can return to the buy area within a set amount of time to buy more equipment (some custom maps included neutral "buy zones" that could be used by both teams). Once the round has ended, surviving players retain their equipment for use in the next round; players who were killed begin the next round with the basic default starting equipment.