Counter-Strike (also marketed as Half-Life: Counter-Strike) is a multiplayer first-person shooter initially created by Minh Le and Jess Cliffe as a mod for Half-Life. By the fifth beta, Valve Software started actively participating in the development and ultimately bought the rights to the game and offered the original developers jobs at the company which both of them accepted. The fast-paced and team-oriented gameplay of Counter-Strike has stayed relatively the same throughout the years. In it, two teams, the Counter-Terrorists and the Terrorists, fight to complete an objective or eliminate the opposing team. Although basic, it is considered one of the most revolutionary online games of all time. The original Counter-Strike came exclusively with multiplayer, without computer-controlled players. Over time, however, several server-side modifications have added bots for in-game use and bots were officially introduced in its later successors, Counter-Strike (Xbox) and Counter-Strike: Condition Zero. Counter-Strike has been praised worldwide for its highly competitive multiplayer. The decision to make the game multiplayer only roots back to its mod origins.

Doing a single-player game would have entailed much more work as new models and AI code would have been needed for enemies as opposed to a multiplayer game which requires considerably less work. There are three official scenarios, each with their own teams, objectives, and maps. In all cases, the two teams are the Counter-Terrorists face off against the Terrorists. In the original retail release, a short single-player only training map was included but this was removed when the game was transferred to Steam. There are three official scenarios in Counter-Strike: Assassination, hostage rescue and bomb defusal. A fourth scenario, known as escape, existed during the Counter-Strike Beta. The scenario itself is still playable, but all of the official maps were removed prior to the game’s release. In this scenario hostages are being held by the Terrorists. Official maps feature between 3 and 5 hostages, though most maps feature 4 hostages. The Counter-Terrorist team needs to rescue these hostages by escorting them to a hostage rescue zone.

The Terrorists must prevent the hostages from being rescued. Victory can also be attained by eliminating the opposing team. This scenario features two bombsites and one Terrorist starts off with a C4. The bomb must be planted at either bombsite. After the bomb has been planted, it will explode after a certain amount of time. During this time, Counter-Terrorists may attempt to defuse the bomb and successful defusal will make the Counter-Terrorists victorious. If the bomb explodes, the Terrorists will win the round. It is also possible to win a round by eliminating the opposing team. This scenario is the least popular of the three and only a single map, Oilrig, is featured in the latest release of the game. In this scenario a single player on the Counter-Terrorist team takes the role of a VIP that must make it to a VIP escape zone. Some maps feature only one escape zone while others feature multiple escape zones.

The Terrorists have to take out the VIP and successfully eliminating the VIP will yield victory to the Terrorists. Both teams have a restricted arsenal of weapons available for purchase. Like in other scenarios, victory can also be attained by eliminating the opposing team. Counter-Strike features a large variety of maps that take place in different environments including urban, arctic, jungle and desert settings. During the post-beta stages, maps were still rotated in the official distribution on a slightly smaller scale. Since the release of Counter-Strike 1.6, no maps have been added or removed from the game. It should be noted that the majority of maps for the game were created by people that were originally simply hobbyist mappers. When Valve Software later bought the rights to Counter-Strike and its content these became the first works published at retail for many of the level designers. There are 25 official maps in the latest version of Counter-Strike. This map was exclusive to the mod edition of the game.

Counter-Strike features a variety of weapons, ranging from knives to shotguns and submachine guns. There was also grenade launchers,such as the HK69, but were removed in later development.The weapons for Counter-Strike were chosen mainly based on two criteria. For one, the weapons had to be satisfying to use and they had to look and sound cool. The other criteria was realism and what weapons the factions would likely be using in real-life. The former of these criteria was given more weight than ensuring authenticity. Inspiration for potential weapon candidates were taken from various movies. For example, the movie Ronin inspired the inclusion of the Krieg 552 and M249. Further inspiration was also taken from the movies Air Force One and the Professional. Most of the information regarding the weapons themselves was sourced from the internet or from gun magazines. Because limited information was available regarding some of the weapons, Minh Le had to guess how some weapons could have functioned when animating them and thus a few weapon models exhibit differences when compared to their real-world counterparts.