This document provides an introduction to a book on the origin of religion. It summarizes that there are two main theories on the origin of religion - theistic and anti-theistic. The book aims to study the origin and early history of religion using the historical method rather than relying on scripture or dogma. It outlines that the book will examine evidence that monotheism preceded polytheism in many early cultures and religions, contradicting the evolutionary view. The introduction concludes by stating the book will argue that the history of religion has been one of decline from an original primitive revelation, not continuous evolution.