Valve acquires the rights to Counter-Strike, originally a Half-Life mod, and officially supports its development. They also produce Half-Life expansions such as Opposing Force and Blue Shift. Valve releases Team Fortress Classic.

Valve launches Steam, initially as a platform to distribute updates and patches for its games. It gradually evolves into a digital distribution platform for third-party games. This is a pivotal decision that fundamentally changes the gaming landscape.

Half-Life 2 is released, further solidifying Valve's reputation for innovation and quality. The game features advanced graphics, physics, and AI, pushing the boundaries of gaming technology.

Steam's library of games expands significantly, attracting both independent and AAA developers. Valve introduces new features like Steamworks, which provides tools and services for developers to integrate their games with Steam.

Valve releases The Orange Box, a compilation that includes Half-Life 2: Episode Two, Team Fortress 2, and Portal. The Orange Box is critically acclaimed and commercially successful.

Left 4 Dead 2 is released, building on the successful co-operative gameplay of the original Left 4 Dead.

Portal 2 is released to critical acclaim, expanding upon the puzzle gameplay mechanics of the original Portal.