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X-COM: UFO Defense cover art
X-COM: UFO Defense. X-COM: UFO Defense artwork, via IGDB. Unofficial site, not affiliated with the publisher.
PC port · MS-DOS → PC

OpenXcom (UFO: Enemy Unknown and Terror From the Deep)

An open-source clone of UFO: Enemy Unknown (X-COM: UFO Defense) and Terror From the Deep for Windows, Mac and Linux, with bug fixes, high resolutions and hundreds of mods. Needs your own game files.

WorkingEngine rewriteNeeds your own copyv1.0 (nightly builds recommended)Updated

You need your own copy of X-COM: UFO Defense. This port only runs with files from a copy you own; there is no download or play button here. No copy? These play in your browser right away, no files needed: BO1 Zombies (vel.gg), GTA 3 Online (quenq III Web), The Simpsons: Hit & Run WASM.

What you need

Unmodified data files from your own UFO: Enemy Unknown / X-COM: UFO Defense and/or X-COM: Terror From the Deep (the Steam releases work and are detected automatically on Windows), plus a Windows, Mac or Linux computer.

GitHub repository ↗

We do not host any files. Only download from the project's official source.

Every version of X-COM: UFO Defense 1

  1. OpenXcom (UFO: Enemy Unknown and Terror From the Deep)This page

    WorkingEngine remake

    Open-source clone of the original X-Com 👽

    Runs on Windows, macOS, Linux and BSDNeeds files from a copy you own★ 2.2k1.0 (nightly builds recommended) · Jun 13, 2014

    Website ↗

We link to each project's own page and host no game files. Version data from project pages, our daily checks and awesome-decomp-games (CC0).

Short answer

OpenXcom is a free, open-source clone of UFO: Enemy Unknown (released in the US as X-COM: UFO Defense) and X-COM: Terror From the Deep, for Windows, macOS and Linux. It fixes the originals’ bugs, runs at modern resolutions and has hundreds of mods. You need the data files from your own copy; the Steam versions are detected automatically.

This site is not affiliated with OpenXcom, MicroProse or 2K. We do not host any files and only link the project’s official pages.

What it is

UFO: Enemy Unknown (1994) and its sequel Terror From the Deep (1995) are MicroProse’s original turn-based X-COM games. The versions sold today run in DOSBox and keep the original bugs, such as the notorious difficulty bug that reset the game to the easiest level after the first mission.

OpenXcom is “an open-source clone of the popular ‘UFO: Enemy Unknown’ (‘X-COM: UFO Defense’ in the USA release) and ‘X-COM: Terror From the Deep’ videogames by Microprose, licensed under the GPL and written in C++ / SDL” (OpenXcom README). It was written from scratch and reads the graphics, sounds and data of your original games. The repository has existed since 2011.

Current status

  • Status: Working. The game has been complete for years; the repository was last updated on 28 September 2026.
  • Releases: the formal 1.0 came out in 2014. The download page also offers nightly builds, which include later fixes and Terror From the Deep support, and are what most players use today.
  • Platforms: Windows, macOS and Linux/BSD.
  • Mods: a mod portal with hundreds of mods, plus standard mods bundled with the game.

What you need

  • Unmodified data from your own copy of UFO: Enemy Unknown / X-COM: UFO Defense, Terror From the Deep, or both. The Steam releases work.
  • A Windows, Mac or Linux computer. Requirements are minimal.

The README is specific: “Do not use modded versions (e.g. with XcomUtil) as they may cause bugs and crashes.”

How setup works (overview)

  1. Install X-COM: UFO Defense and/or Terror From the Deep (for example from Steam).
  2. Download OpenXcom from the download page; a nightly build is recommended.
  3. On Windows, run the installer: it finds Steam copies and copies the game data for you.
  4. Otherwise copy the data yourself: the contents of Steam\SteamApps\common\XCom UFO Defense\XCOM into OpenXcom’s UFO folder, and X-COM Terror from the Deep\TFD into its TFTD folder.
  5. Start OpenXcom, pick the game, and set resolution and options.

What it adds

  • Original bugs fixed, including the difficulty reset, while keeping the original rules.
  • Any resolution, windowed or fullscreen.
  • Interface improvements, such as better base and equipment screens and more information in battle.
  • Bundled standard mods based on XcomUtil and UFO Extender features, switchable in Options > Mods.
  • Mod support through the mod portal, from small tweaks to total conversions.

Mods and OXCE

To install a mod, extract it into its own folder under mods in your OpenXcom user folder, make sure its contents (such as Rulesets) are at the top level, and enable it in Options > Mods.

Many of the biggest mods need OpenXcom Extended (OXCE), a fork that adds modding features. If a mod’s page says it requires OXCE, use that build instead; your original game data works the same way.

Common problems

  • “Missing files” on start: the game data is not in the UFO or TFTD subfolder, or it came from a modded copy.
  • A mod fails to load: its folder structure has an extra level (for example mods/Name/data/Rulesets); move everything up one level, as the README describes.
  • Old guides mention only UFO: Terror From the Deep support is in the nightly builds, not 1.0.

FAQ

How do I play the original X-COM on Windows 10 or 11?

Use OpenXcom. Install X-COM UFO Defense (and Terror From the Deep if you have it) from Steam, then run the OpenXcom Windows installer, which detects the Steam games and copies their data automatically. The game then runs natively at modern resolutions.

Does OpenXcom need the original game?

Yes. It requires the unmodified data files from UFO Enemy Unknown (X-COM UFO Defense), Terror From the Deep, or both. The README warns not to use copies modified with XcomUtil, as they can cause bugs and crashes.

Does OpenXcom support Terror From the Deep?

Yes. OpenXcom plays both UFO Enemy Unknown and X-COM Terror From the Deep. You copy each game's data into its own subfolder (UFO and TFTD).

Should I use OpenXcom 1.0 or a nightly build?

The download page offers both. Version 1.0 dates from 2014, and the project's newer nightly builds include years of fixes and Terror From the Deep support, so most players and mods use a recent nightly.

What is OXCE?

OpenXcom Extended, a fork of OpenXcom that adds many modding features. Large total conversions such as The X-Com Files and XPiratez are built for it. It uses the same original game data.

Unofficial. This page is written by an independent directory. It is not made by, endorsed by or affiliated with MicroProse (now Take-Two / 2K) or OpenXcom developers (OpenXcom (UFO: Enemy Unknown and Terror From the Deep)'s author). We do not host any files, and we never link to game files, ROMs or ISOs.

Sources

This page was last updated on Nov 3, 2026. A date after a source is the day we read it. Versions and steps follow the official project; if they differ, the official source wins.

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