At strategic scale, the player directs the research and development of new technologies, builds and expands X-COM's bases, manages the organisation's finances and personnel, and monitors and responds to UFO activity.

[3] Each ground mission takes place within a procedurally-generated, voxel-based 3D map, evenly divided into square-bottom cubes and vertical layers for gameplay purposes.

The Battlescape's turn-based system uses action points, known in the game as Time Units (TUs), that are distributed between individual soldiers according to their statistics (including the total weight of carried equipment relative to their strength, and the top and current levels of stamina).

Each turn, their TUs can be spent for movement and a variety of actions (through an icon-based GUI), such as firing weapons, managing their equipment including ammunition (items carried in hands, pockets, belt, and backpack), picking up or throwing objects (limited in this to friendly or enemy equipment or bodies), kneeling down, using items, reloading weapons, and priming explosives.

A major feature called Opportunity Fire enables combatants to automatically shoot at a spotted hostile during the enemy turn if enough of their TUs have been reserved and left unspent.

[7] Instead of gaining experience points, surviving human combatants might get an automatic rise (a semi-random amount depending on how much of the action in which they participated) to their attributes, such as Psi or Accuracy.

In addition to combat personnel, the player may use unmanned ground vehicles that are outfitted with heavy weapons and well armored but large, costly, and not gaining experience.

Although supportive of the project, the publisher expressed concerns that the demo lacked a grand scale in keeping with MicroProse's hit strategy game Civilization.

[1] Under MicroProse's direction and working at its Chipping Sodbury studio,[11] Julian Gollop said that while the research and technology tree somewhat emulates the role of advances in Civilization, "it also helped to develop the storyline.

[15] A book by Bob Lazar, where he describes his supposed work with recovered UFOs at Area 51, inspired the concept to reverse-engineer captured alien technology.

[9] His sources of inspirations for the game also included Whitley Strieber's book Communion and other "weird American stories",[15] as well as the Alien film series.

Julian Gollop credited Reitze, who also designed the alien races,[17] with "a distinctive comic book style", and Smillie with "very detailed environment graphics".

[1] MicroProse musician John Broomhall, inspired by Bernard Herrmann's score in the film Psycho,[18] composed the original soundtrack of the PC version while Andrew Parton handled the sound effects.

Besides Moreland, there were other MicroProse employees not acknowledged in the game's credits despite having been major contributors to its development, such as assisting designers Mike Brunton and (especially) Steve Hand.

[1] Certain creature types deemed boring were removed during the development, as were the Men in Black, who have been left unused due to a perceived conflict with MicroProse's abortive project to make an MIB-themed standalone game.

[1][19] A public demo of the game was released in Europe under the name UFO: Enemy Unknown in April 1994,[20] and in North American in May 1994 under the then-working title X-COM: Terran Defense Force.

[21] Despite numerous changes from the first demo, the tactical part of the game remains true to the turn-based layout of Laser Squad and the Gollop brothers' earlier Rebelstar series.

[9] The AI system of those games formed the basis for enemy tactics, with Julian Gollop programming his own unique algorithms for pathfinding and behavior; in particular, the aliens were purposely given an element of unpredictability in their actions.

[23] However, Moreland held a meeting with other MicroProse UK bosses Adrian Parr and Paul Hibbard, where they decided to ignore it and would simply not inform the Gollop brothers and others involved in the project about any of that.

[1] During the final three months, after Spectrum HoloByte was eventually informed of the game still being in production, the Gollop brothers were forced to work 7–12 in order to finish it before the end of the fiscal year.

[37] According to Rock, Paper, Shotgun's negative review of Duane's novel, it is hampered by a poor understanding of the game, a lack of focus, emotional resonance and tension, and an unstructured plot.

This glitch was not noticed by MicroProse and was not fixed in the official patches, resulting in the very high difficulty of the sequel[4] due to many complaints from veteran players who believed that the original game was still too easy even on seemingly higher levels.

[41] OpenXcom is an open-source reimplementation of that game to fix all the known bugs and limits, improve the AI and user interface, localise in more languages, and to provide cross-platform builds, e.g. for Linux and Android.

Describing it as "one of those rare and dangerous games capable of drilling into your brain, putting a vice-grip on your imagination, and only releasing you when it has had enough," the magazine praised its detailed and varied combat system and lengthy gameplay, concluding "Resistance is futile".

[48] GameSpot review described UFO: Enemy Unknown as "a bona fide modern classic, standing proudly alongside Civilization and Populous as a benchmark in the evolution of strategy gaming.

However, he praised the game itself for sophisticated, enjoyable gameplay, and concluded that UFO: Enemy Unknown was "a smashing PC title, it's lost nothing of practical value in the translation, and makes a marvelous addition to the console market.

"[30] GamePro disagreed, stating that "You have to be a major sim-freak to enjoy" UFO: Enemy Unknown, and saying that "It's an interesting and complex game about planet colonising, [sic] but the extensive manuals and one-dimensional music really bore you to alien tears after a while.

"[104] In 2012, including it among the most essential game of all time, 1UP.com commented that "with its unrivaled balance of tactics and tension, [UFO: Enemy Unknown] remains a masterpiece.

[107] 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, titled XCOM: Enemy Unknown, was developed by Firaxis Games, led by MicroProse's co-founder Sid Meier.