The story of X-COM, set in the near-future at the time of the game's release, begins in the year 1998.

Gollop's new X-COM spiritual successor project, Phoenix Point, was released in 2019. Mythos Games' and Julian Gollop's own original spiritual successor project, The Dreamland Chronicles: Freedom Ridge, was cancelled in 2001 and later partially turned into UFO: Aftermath by another developer. An official remake of the game, XCOM: Enemy Unknown, was created by Firaxis Games and published by 2K Games in 2012. It was the first and best-received entry in the X-COM series and has directly inspired several similar games, including UFO: Alien Invasion, UFO: Extraterrestrials and Xenonauts. The game received strong reviews and was commercially successful, acquiring a cult following among strategy fans several publications have listed X-COM: UFO Defense as one of the best video games ever made, including IGN ranking it as the best PC game of all time in 2007. At strategic scale, the player directs the research and development of new technologies, builds and expands X-COM's bases, manages the organization's finances and personnel, and monitors and responds to UFO activity. Through the game, the player is tasked with issuing orders to individual X-COM troops in a series of turn-based tactical missions. The player takes the role of commander of X-COM – an international paramilitary organization secretly defending Earth from an alien invasion. Originally planned by Julian Gollop as a sequel to Mythos Games' 1988 Laser Squad, the game mixes real-time management simulation with turn-based tactics. It was published by MicroProse for DOS and Amiga computers, the Amiga CD32 console, and the PlayStation. X-COM: UFO Defense (known as UFO: Enemy Unknown in Europe) is a 1994 science fiction strategy video game developed by Mythos Games.

Xcom tech tree enemy within