“The Sophists” generally refers to Protagoras, Gorgias, Hippias, Prodicus, and Antiphon, as well as to a few lesser-known fifth-century figures; but why it does so, and what holds these men together, has been a matter of debate from Plato’s time to our own. Neither of the two standard explanations fit all and only these figures – the philosophical one, that they share some revolutionary epistemological outlook (for instance, relativism or anti-realism), or the sociological one, that they are primarily teachers of virtue of pay. This Introduction proposes revisiting the Sophists as celebrated instances of their time, a period of energetic intellectual discovery, experimentation, and communication. Doing so opens new questions about their continuity with their background culture as well as any distinctive interests, methods, or beliefs they might have. The Introduction goes on to discuss all early uses of the term sophistês in the fifth century (from Pindar through Thucydides) and its dominant uses in the fourth century, allowing us to see the range of kinds of people it applied to and the force with which it was applied. Then it describes the heterogeneous evidence base for Sophists and cognate figures. It concludes with a summary of the volume’s chapters.