XCOM (originally called X-COM) is a science fiction video game franchise featuring an elite international organization tasked with countering alien invasions of Earth.

The X-COM series, in particular its original entry, achieved a sizable cult following and has influenced many other video games; including the creation of a number of clones, spiritual successors, and unofficial remakes.

The premise of the franchise is that an alien invasion beginning in 1999 prompts the creation of a clandestine paramilitary organization codenamed X-COM (an abbreviation of "Extraterrestrial Combat") by a coalition of funding nations.

[9] The first sequel, Terror from the Deep, was quickly created by MicroProse's internal team; based on the same game engine and used largely identical gameplay mechanics.

Apocalypse took several new directions with the series, introducing an optional real-time combat system and shifting the aesthetics to a retro-futuristic style.

In 2001, Hasbro published X-COM: Enforcer, a poorly received third-person shooter loosely based on the events of Enemy Unknown, marking a low point in the series.

Terry Greer, a former senior artist and head of game design at MicroProse UK, disclosed: "We'd also discussed other avenues for future games including time travel, retaking the solar system (with interplanetary distances playing a significant role in recruitment and resources), and resistance movement concept where you had to fight back after the world was taken and humanity was totally under the alien yoke.

"[14] OpenXcom is an open source re-implementation of the first game in the series intended to fix all the bugs and enable modding.

The setting received a complete overhaul, now based in the early 1960s, with the original XCOM organization being a secret U.S. federal agency.

Originally planned for 2011, the game was repeatedly redesigned by different studios before being finally released in 2013 as The Bureau: XCOM Declassified for Windows, OS X, PlayStation 3 and Xbox 360.

[1] It was released in 2016 for Windows, PlayStation 4, Xbox One, OS X, and Linux (Later ported to several other platforms, including the Nintendo Switch, but not iOS).

MicroProse's manual/documentation writer John Possidente also wrote three short stories, "Decommissioning", "Manley's Deposition", and "Moray in the Wreck", taking place between the events of the first two games in the series.

According to Julian Gollop, "They wanted us to do a deal where we would sign over any rights that we might have in return for some cash plus a high royalty on X-COM: Apocalypse.

The franchise was also referenced in the Civilization series of strategy video games that had partially inspired X-COM in first place.