From Socrates and Plato onwards, the Sophists were often targeted by the authoritative philosophical tradition as being mere charlatans and poor teachers. This book, translated and significantly updated from its most recent Italian version (2nd edition, 2013), challenges these criticisms by offering an overall interpretation of their thought, and by assessing the specific contributions of thinkers like Protagoras, Gorgias and Antiphon. A new vision of the Sophists emerges: they are protagonists and agents of fundamental change in the history of ancient philosophy, who questioned the grounds of morality and politics, as well as the nature of knowledge and language. By shifting the focus from the cosmos to man, the Sophists inaugurate an alternative form of philosophy, whose importance is only now becoming clear.