Alien is a science-fiction horror and action media franchise centered on the film series which depicts warrant officer Ellen Ripley (Sigourney Weaver) and her battles with an extraterrestrial lifeform, commonly referred to as "the Alien" or Xenomorph.

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 a prequel series, composed of Prometheus (2012) and Alien: Covenant (2017), which follows the exploits of the David 8 android and the creators of the eponymous creatures referred to as the "Engineers".

The series has led to numerous novels, comics, video games and an upcoming television series 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 series of comics, books, and video games.