Alien is a science fiction horror and action media franchise centred on the original film series, which depicts warrant officer Ellen Ripley (Sigourney Weaver) and her battles with an extraterrestrial lifeform, commonly referred to as the Alien ("Xenomorph"), and the prequel series, which follows the exploits of the David 8 android (Michael Fassbender) and the creators of the eponymous creatures referred to as the Engineers.

Produced and distributed by 20th Century Studios, the series began with Alien (1979), directed by Ridley Scott, and was followed by three sequels: Aliens (1986), directed by James Cameron; Alien 3 (1992), directed by David Fincher, and Alien Resurrection (1997), directed by Jean-Pierre Jeunet. Scott also directed the prequel series films Prometheus (2012) and Alien: Covenant (2017).

The series has led to numerous novels, comics, video games, and an upcoming television series, also titled Alien, developed by Scott for FX on Hulu with Noah Hawley. It has inspired a number of spin-offs—most notably the Alien vs. Predator series, which combines the continuities of the Alien franchise with the Predator franchise and consists of two films as well as various comics, books, and video games.