Sid Meier's Alpha Centauri is a 4X video game, considered a spiritual sequel to the Civilization series. Set in a science fiction depiction of the 22nd century, the game begins as seven competing ideological factions land on the planet Chiron ("Planet") in the Alpha Centauri star system. As the game progresses, Planet's growing sentience becomes a formidable obstacle to the human colonists.

Sid Meier, designer of Civilization, and Brian Reynolds, designer of Civilization II, developed Alpha Centauri after they left MicroProse to join with Jeff Briggs in creating a new video game developer: Firaxis Games. Electronic Arts released both Alpha Centauri and its expansion, Sid Meier's Alien Crossfire, in 1999. The following year, Aspyr Media ported both titles to Classic Mac OS while Loki Software ported them to Linux.

Alpha Centauri features improvements on Civilization II's game engine, including simultaneous multiplay, social engineering, climate, customizable units, alien native life, additional diplomatic and spy options, additional ways to win, and greater mod-ability. Alien Crossfire introduces five new human and two non-human factions, as well as additional technologies, facilities, secret projects, native life, unit abilities, and a victory condition.

The game received wide critical acclaim, being compared favorably to Civilization II. Critics praised its science fiction storyline (comparing the plot to works by Stanley Kubrick, Frank Herbert, Arthur C. Clarke, and Isaac Asimov), the in-game writing, the voice acting, the user-created custom units, and the depth of the technology tree. Alpha Centauri also won several awards for best game of the year and best strategy game of the year.

Space-race victories in the Civilization series conclude with a journey to Alpha Centauri. Beginning with that premise the Alpha Centauri narrative starts in the 22nd century, after the 2060 launch of the United Nations colonization mission "Unity" to Alpha Centauri's planet Chiron ("Planet"). Unbeknownst to humans, advanced extraterrestrials ("Progenitors") had been conducting experiments in vast distributed nervous systems, culminating in a planetary biosphere-sized presentient nervous system ("Manifold") on Chiron, leaving behind monoliths and artifacts on Chiron to guide and examine the system's growth. Immediately prior to the start of the game, a reactor malfunction on the Unity spacecraft wakes the crew and colonists early and irreparably severs communications with Earth. After the captain is assassinated, the most powerful leaders on board build ideological factions with dedicated followers, conflicting agendas for the future of mankind, and "desperately serious" commitments. As the ship breaks up, seven escape pods, each containing a faction, are scattered across Planet.

In the Alien Crossfire expansion pack, players learn that alien experiments led to disastrous consequences at Tau Ceti, creating a hundred-million-year evolutionary cycle that ended with the eradication of most complex animal life in several neighboring inhabited star systems. After the disaster (referred to by Progenitors as "Tau Ceti Flowering"), the Progenitors split into two factions: Manifold Caretakers, opposed to further experimentation and dedicated to preventing another Flowering; and Manifold Usurpers, favoring further experimentation and intending to induce a controlled Flowering in Alpha Centauri's Planet. In Alien Crossfire, these factions compete along with the human factions for control over the destiny of Planet.

The game focuses on the leaders of seven factions, chosen by the player from the 14 possible leaders in Alpha Centauri and Alien Crossfire, and Planet (voiced by Alena Kanka). The characters are developed from the faction leaders' portraits, the spoken monologues accompanying scientific discoveries and the "photographs in the corner of a commlink – home towns, first steps, first loves, family, graduation, spacewalk." The leaders in Alpha Centauri comprise: Lady Deirdre Skye, a Scottish activist (voiced by Carolyn Dahl), of Gaia's Stepdaughters; Chairman Sheng-Ji Yang, a Chinese Legalist official (voiced by Lu Yu), of the Human Hive; Academician Prokhor Zakharov, a Russian academic (voiced by Yuri Nesteroff) of the University of Planet; CEO Nwabudike Morgan, a Namibian businessman (voiced by Regi Davis), of Morgan Industries; Colonel Corazon Santiago, an American militiawoman (voiced by Wanda Niño) of the Spartan Federation; Sister Miriam Godwinson, an American minister and social psychologist (voiced by Gretchen Weigel), of the Lord's Believers; and Commissioner Pravin Lal, an Indian surgeon and diplomat (voiced by Hesh Gordon), of the Peacekeeping Forces.

The player controls one of the leaders and competes against the others to colonize and conquer Planet. The Datalinks (voiced by Robert Levy and Katherine Ferguson) are minor characters who provide information to the player. Each faction excels at one or two important aspects of the game and follows a distinct philosophical belief, such as technological utopianism, Conclave Christianity, "free-market" capitalism, militarist survivalism, Chinese Legalism, U.N. Charter humanitarianism, or Environmentalist Gaia philosophy. The game takes place on Planet, with its "rolling red ochre plains" and "bands of lonely terraformed green".