Half-Life: Decay

Half-Life: Decay is an expansion pack for Valve Software's science fiction, first-person shooter video game Half-Life. Developed by Gearbox Software and published by Sierra Entertainment, Decay was released as part of the PlayStation 2 version of Half-Life released on November 14, 2001. It is the third expansion pack for Half-Life, and like its predecessors, Decay returns to the setting and timeline of the original story, albeit portraying the story from the viewpoint of a different set of protagonists: two scientists working in the Black Mesa Research Facility. Decay is a cooperative multiplayer game, designed to be played by two people working together to pass through the game's levels.

Decay was not a critical success, but was received with some positivity by journalists in the video games industry. Many reviewers felt the game was fun to play through with a friend, but that its more puzzle-orientated gameplay somewhat detracted from the overall experience. A number of reviews stated that the game simply felt little more than an extra add-on for the PlayStation 2 version of Half-Life. In September 2008, a group of Ukrainian developers unofficially ported the game to Windows as a modification of the PC version of Half-Life.