Delta Green is a fictional secret government program that combines elements of horror and espionage. It was originally created for tabletop role-playing games, particularly in the Call of Cthulhu universe, and focuses on agents who combat supernatural threats while dealing with the psychological toll of their missions. The program operates outside normal government channels, often using unconventional methods to confront alien entities and otherworldly horrors. Players take on the roles of agents who must balance their duties with the risks of madness and moral ambiguity, making for a tense and immersive gaming experience.