The book begins with a prologue, in which the author, noted mythologist Joseph Campbell, outlines both his core theory and the literary/analytical process he uses in the book to illuminate it. That theory is that there are three central truths at the core of the spiritual and psychological belief systems of all cultures in all times and in all places: that there is a spiritual world existing in parallel with the physical; that the ultimate goal of physical existence is to connect with that spiritual world; and that truth is both explored and defined through the universal human experience of myth. Campbell also indicates in the prologue that the purpose of the book is to explore the nature of that spiritual world, the ways in which it manifests in the physical world, and the ways in which myth illuminates those manifestations.

At the book's conclusion, Campbell makes the clear statement that contemporary culture in general, and western culture in particular, have over the years moved further and further away from the self-understanding and self awareness to be found in myth. The human experience, he maintains, has become shallower and more superficial, becoming less and less what myth suggests it was intended to be – a true experience of harmony between the physical (that which we can touch, see, smell, hear and taste), and the spiritual (that which, through myth and symbol, we intuitively, psychologically and instinctively feel).”