A shared universe is a fictional universe to which more than one writer contributes. Works set in a shared universe share characters and other elements with varying degrees of consistency. Shared universes are contrasted with collaborative writing, in which multiple authors work on a single story. Shared universes are more common in fantasy and science fiction than in other genres. Examples include Star Trek, DC Universe, Marvel Universe, Star Wars, Forgotten Realms, Babylon 5, Foundation series, Dragonlance, Power Rangers, Man-Kzin Wars, and Cthulhu Mythos.