Alien and Predator owned and produced by 20th Century Studios.

Two monsters. One shared universe. Bad news for humanity. The Alien and Predator movies originally began as separate franchises, though thanks to a small easter egg in Predator 2 and demand to see the creatures clash inevitably led to a mixed universe. Predator films typically take place during the modern era, while Alien films take place in the future, though there is plenty of overlap thanks to the Alien vs. Predator movies.

The release of the game Aliens: Colonial Marines has created a split in the canonical Alien timeline, essentially negating the events of Alien3 (and, in all likelyhood, Alien: Resurrection). Its status as the true sequel to Aliens is up to debate, however, as Aliens: Colonial Marines was poorly-received, and the new timeline it seemed to be setting up has been abandoned. 

There have been a significant number of books, comics, and video games that further expand the Alien and Predator universes. There are so many, in fact, that they often contradict one another. For the most part this list ignores those entries, aside from Alien: Isolation and Aliens: Colonial Marines. Please consult this page for a more in-depth listing of media related to the Alien and Predator franchises.

In-Universe Chronological Order - Combined timeline
or
Release Order