UFO: Enemy Unknown (X-COM: UFO Defense)

The game takes place within two distinct views, called the Geoscape and the Battlescape. According to GameSpy, "Playing it again in 2012, it comes off as both completely brilliant and slightly insane. In effect, X-COM melds an SSI Gold Box RPG with a highly detailed 4X game like Master of Orion, making it in some ways two entirely different games."

The game begins on January 1, 1999, with the player choosing a location for their first base on the Geoscape screen: a global view representation of Earth as seen from space (displaying X-COM bases and aircraft, detected UFOs, alien bases, and sites of alien activity). The player can view the X-COM bases and make changes to them, equip fighter aircraft, order supplies and personnel (soldiers, scientists and engineers), direct research efforts, schedule manufacturing of advanced equipment, sell alien artifacts to raise money, and deploy X-COM aircraft to either patrol designated locations, intercept UFOs, or send X-COM ground troops on missions using transport aircraft.