This book is not about delusion about God, nor is it about deception about God. It is about those authors who use scientific-like language in order to propagate religious ideas, and by doing so, they consciously or unconsciously deceive their readers. This is the reason choosing the word "deception" in the book's title, and enclosing the words "Science of God" in quotation marks to emphasize that there is no such thing as "Science of God." To put it differently, the "Science of God," in the book's title was chosen to imply that the greatest deception involves the (non-existent) "Science of God." The first part describes the author's view on the various deceptive arguments presented in the literature about the existence of God. The second part consists of 25 critical reviews of books dealing with topics related to "Science of God."