A book by Joseph Campbell that proposes that most mythical heros are all examples of a hero archetype. It proposes that heroic myths are instances of the monomyth. The story goes somthing like this:

1. Separation: The hero goes off somewhere. This can be voluntary, or involuntary.
2. Transformation: The hero is in some way changed, internally or externally.
3. Return: The hero returns to his society, changed.

Classic examples include Orpheus, Star Wars and Ulysses.
Many cultures base initiation ceremonies on the monomyth.