This book deals with popular Orthodoxy during the Byzantine and Ottoman periods, approaching the material from a historical and anthropological perspective. The discussion takes as its starting point a letter of Leo Allatios, the seventeenth-century author and scriptor of the Vatican Library. The early chapters of the book focus on Allatios and the western intellectual background in which the work was written, while later chapters consider popular beliefs and practices surrounding childstealing demons, revenants, spirits of place and popular healing. This book provides the first detailed treatment of a major source for post Byzantine popular Orthodoxy, offering valuable insights into the relationships between laity and clergy, Orthodoxy and Catholicism, religion and natural philosophy during the seventeenth century.