This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book is a collection of essays, all of them revised and some of them unpublished, about theories of myth. It complements my 1999 collection Theorizing about Myth. In the first chapter of the present collection, the author surveys the main theories from the past century and a half. In the remaining chapters, the author analyzes specific theories or groups of theories. Theories of myth consider three main questions: what is the origin, what is the function, and what is the subject matter of myth? Origin means why and how myth arises. First, the scope of theories is worldwide, whereas that of transmission tends to be regional. Second, the explanations of similarities given by theories are based on regularities, whereas the explanations given by transmission are happenstance.