Amulets in the Greco-Roman world came in many different forms and were used in many different contexts. The ubiquity of amulets in the Greco-Roman world is hardly in doubt, and this in itself suffices to prove that they were deemed to be effective protectors against dangerous forces. But why were they deemed powerful, and where, from the perspective of their producers and users, did these powers come from? To answer such questions, this chapter explains both the archaeological record and the literary evidence, which complement each other in telling us not only what people did, but also why they did it. It examines the evidence for uninscribed amulets and inscribed amulets. The chapter turns to three related issues: the amulets’ physical use (or embodiment), the metaphysical assumptions undergirding the recourse to amulets in antiquity, and the social realia lying behind them and sometimes reflected by them.