Religion is relevant to all of us, whether we are believers or not. This book concerns two interrelated topics. First, how probable is God's existence? Should we not conclude that all divinities are human inventions? Second, what are the mental and social functions of endorsing religious beliefs? The answers to these questions are interdependent. If a religious belief were true, the fact that humans hold it might be explained by describing how its truth was discovered. If all religious beliefs are false, a different explanation is required. In this provocative book Herman Philipse combines philosophical investigations concerning the truth of religious convictions with empirical research on the origins and functions of religious beliefs. Numerous topics are discussed, such as the historical genesis of monotheisms out of polytheisms, how to explain Saul's conversion to Jesus, and whether any apologetic strategy of Christian philosophers is convincing. Universal atheism is the final conclusion.