Click here for an explanation of the traditional approach to the notion of the Monomyth (first formulated by Joseph Campbell in his landmark book, The Hero with a Thousand Faces).
Click here for a formulation of the Monomyth as revised by John T. Kirby -- based on the Campbell model, but streamlined in some respects (so as to accommodate more types of tale and more artistic genres, including screen media) and augmented in others (so as to take account of certain folklore elements, and of the involvement of the reader/audience).