Which 2004 game introduced the Source engine to the Counter-Strike series?

Counter-Strike: Source introduced Valve’s Source engine to the Counter-Strike series in 2004.

Counter-Strike: Source was developed by Valve and Turtle Rock Studios as a remake of the original Counter-Strike. It replaced the older GoldSrc technology with Source, Valve’s newer engine, which supported updated lighting, physics, character models, and map presentation. The game retained the team-based tactical structure and bomb-defusal and hostage-rescue scenarios that defined the series.

The title was released for Windows in October 2004 and was initially bundled with Half-Life 2. Its use of physics-based objects and improved visual effects made it noticeably different from Counter-Strike 1.6, although both games remained available and developed separate player communities.

Counter-Strike: Source is often confused with Counter-Strike: Global Offensive, which arrived in 2012 and used a later branch of Source. Counter-Strike 2, released in 2023, moved the series to Valve’s Source 2 engine instead.