UFO: Alien Invasion is a squad-based tactical strategy game in the tradition of the old X-COM PC games. It combines military realism with hard science-fiction and the weirdness of an alien invasion. The carefully constructed turn-based system gives you pin-point control of your squad while maintaining a sense of pace and danger.

UFO:AI has two main modes of play: Geoscape mode and Tactical mode.

In Geoscape mode you manage the activities and finances of PHALANX, a secret organisation charged with defending Earth from a brutal alien enemy. You control bases, installations, aircraft and squads of armed-response troops. You will research new technologies and use their results in battle against the aliens. You can build, buy and produce anything you like, as long as your technology level and your budget will allow it. Easy-to-use time buttons make it possible to control the passage of time.

In Tactical mode the game is about taking command of your team in various missions to combat the aliens wherever they might appear. Tactical mode uses a turn-based system, where your team and the aliens take turns to make moves. You can order your troops around, fire their weapons, throw grenades and use other equipment. All actions require Time Units to perform. Once a soldier is out of Time Units, he or she can't do anything more until the next turn. Your mission objectives will vary for each mission and there are many to perform as the aliens' terrifying plot unfolds. You'll have to watch your back, be quick on your feet and take the fight to them.

If you don't, humanity is doomed.