In this book, Phillip Wiebe examines religious, spiritual, and mystical experiences, assessing how these experiences appear to implicate a spiritual order. Despite the current prevalence of naturalism and atheism, he argues that experiences purporting to have a religious or spiritual significance deserve close empirical investigation. Wiebe surveys the broad scope of religious experience and considers different types of evidence that might give rise to a belief in phenomena such as spirits, paranormal events, God, and an afterlife. He demonstrates that there are different explanations and interpretations of religious experiences, both because they are typically personal accounts, and they suggest a reality that is often unobservable. Wiebe also addresses how to evaluate evidence for theories that postulate unobservables in general, and a Theory of Spirits in particular. Calling for more rigorous investigation of these phenomena, Wiebe frames the study of religious experience among other accepted social sciences that seek to understand religion.