The Roman author Pliny the Younger characterizes Christianity as "contagious superstition"; two centuries later the Christian writer Eusebius vigorously denounces Greek and Roman religions as vain and impotent "superstitions." The term of abuse is the same, yet the two writers suggest entirely different things by "superstition." Dale Martin provides the first detailed genealogy of the idea of superstition, its history over eight centuries, from classical Greece to the Christianized Roman Empire of the fourth century C.E. With illuminating reference to the writings of philosophers, historians, and medical teachers he demonstrates that the concept of superstition was invented by Greek intellectuals to condemn popular religious practices and beliefs, especially the belief that gods or other superhuman beings would harm people or cause disease. Tracing the social, political, and cultural influences that informed classical thinking about piety and superstition, nature and the divine, exposes the manipulation of the label of superstition in arguments between Greek and Roman intellectuals on the one hand and Christians on the other, and the purposeful alteration of the idea by Neoplatonic philosophers and Christian apologists in late antiquity. weaves a powerfully coherent argument that will transform our understanding of religion in Greek and Roman culture and the wider ancient Mediterranean world.