Shared universe

A Shared universe is a literary technique in which several different authors share settings and characters which appear in their respective works of fiction, often referring to events taking place in the other writers' stories. It can also be called a "shared setting." It can be a metafictional device. Shared fictional universes tend to appear more frequently in fantasy and science fiction than in other genres.

Posthumous retroactive shared worlds

• August Derleth and others wrote stories which connected the Conan the Barbarian stories by Robert E. Howard with the 1920's era Cthulhu Mythos stories of H. P. Lovecraft, and some stories by Clark Ashton Smith, placing them in a shared fictional universe along with Derleth's own new Cthulhu Mythos stories. Some argue that the Cthulhu Mythos itself is Derleth's invention, and that Lovecraft did not actually intend to set these stories in a common world.
• Ruth Plumly Thompson and various other authors wrote sequels to L. Frank Baum's Oz stories.
• Greg Bear, Gregory Benford, and David Brin wrote novels set in Isaac Asimov's Foundation universe.