XCOM: Enemy Unknown

XCOM: Enemy Unknown casts the player as the commander of an elite military organization who directs soldiers in turn-based combat missions against invading alien enemies. The player controls a squad of between one and six human soldiers or robotic units as they explore the game's levels. Most missions in the campaign occur on maps randomly selected from a handcrafted set; enemies are then randomly placed on these maps. Fog of war hides aliens and their actions from view until the player's soldiers are in range and have line of sight to them.

Most missions require players to eliminate all threats in a map, though some require players to rescue civilians or extract a target. Players can choose to retreat and abandon the mission if the situation goes awry. The game has four difficulty levels: easy, normal, classic and "impossible". There is also an "ironman mode", which limits the player to one save.

The game's campaign begins in early 2015 as a global alien invasion begins. Prior to the start of the game, a group of countries called the Council of Nations has banded together to create Extraterrestrial Combat Unit (XCOM), the most elite military and scientific organization in human history that is tasked with defending the nations from alien attack. The player assumes the role of the commander of XCOM and engages in a war against an extraterrestrial enemy with overwhelming technological superiority.

In March 2015, a series of extraterrestrial objects land in a major German city. A squad of four soldiers is sent to investigate the incident. Upon entering a warehouse, the squad finds a small, alien creature mind-controlling German soldiers. The squad is ambushed; all-but-one of the soldiers are killed before the area is secured. Alien attacks begin all over the globe.

Development of XCOM: Enemy Unknown commenced at Firaxis Games in early 2008 as a "very, very big budget" project with a team of 50 to 60 developers. XCOM: Enemy Unknown was developed independently of 2K Marin's XCOM, which was later rebranded as The Bureau: XCOM Declassified, and although the two games are set in different universes, the games' developers were in contact with one another. Enemy Unknown was the first title Firaxis Games developed that did not feature the name of Sid Meier, who was not directly involved in the game's development.

Being a fan of UFO: Enemy Unknown (1994), director Jake Solomon had repeatedly petitioned Firaxis' leaders to create a sequel since he joined the studio. In 2003, Solomon was given six months to lead a team and develop a prototype for an XCOM game. He and other programmers quickly wrote a game engine using assets from media such as Unreal Tournament. In this early demo, which used an extensive inventory-management system, players explored a large, open area and eliminated alien threats.

According to review aggregator website Metacritic, XCOM: Enemy Unknown received "generally favourable reviews" from critics. Franchise creator Julian Gollop also praised the game, describing it as an "addictive and absorbing" experience; he liked the new alien design and enjoyed the challenging gameplay.

Evan Lahti from PC Gamer praised Firaxis for understanding the core gameplay pillars of the franchise and modernizing them for a new audience, resulting in a combat system that was "more coherent and elegant" than similar games in the same genre. He also liked the way the combat captured the "childlike joy" of moving a squad of action figures. Dan Stapleton from GameSpy described the game as "an amazingly addictive, challenging, and rewarding experience", praised its improvements over the gameplay of UFO: Enemy Unknown, and said its difficulty and randomness made it highly replayable. Kevin VanOrd from GameSpot wrote that the randomness of combat heightened the tension and anxiety, and the cinematic camera "[dramatized] the successes and failures".

The game, which was released when interest in turn-based strategy games was low, introduced the genre to a new generation of players. PC Gamer's Fraser Brown, in a 2019 article, wrote that XCOM: Enemy Unknown "came along and lit a fire under the genre, arguably kicking off the decade of turn-based tactics games". The term "XCOM" became synonymous with the genre. In October 2022, Alex Donaldson from VG247 described the game as "the best franchise reboot of all time", praising Firaxis' ability to recapture the essence of the original game while modernizing it for a new generation of audience.

Firaxis developed a sequel to XCOM: Enemy Unknown titled XCOM 2. The game takes place 20 years after the events of Enemy Unknown; its story is an alternative scenario in which XCOM failed to stop the alien invasion and humanity surrendered. The player controls a small resistance movement fighting the alien conquerors. XCOM 2 was released for Windows in February 2016 and for consoles in September the same year.