From student protests over the teaching of canonical texts such as Plato’s Republic to the use of images of classical Greek statues in white supremacist propaganda, the world of the ancient Greeks is deeply implicated in a heated contemporary debate about identity and diversity. Plato’s Caves defends the bold thesis that Plato was a friend of cultural diversity, contrary to many contemporary perceptions. It shows that, across Plato’s dialogues, foreigners play a role similar to that of Socrates: liberating citizens from intellectual bondage. Through close readings of four Platonic dialogues—Republic, Menexenus, Laws, and Phaedrus—the author recovers Plato’s unique insight into the promise, and risk, of cross-cultural engagement. Like the Socratic “gadfly” who stings the “horse” of Athens into wakefulness, foreigners can provoke citizens to self-reflection by exposing contradictions and confronting them with alternative ways of life. The painfulness of this experience explains why encounters with foreigners often give rise to tension and conflict. Yet it also reveals why cultural diversity is an essential good. Simply put, exposure to cultural diversity helps one develop the intellectual humility one needs to be a good citizen and global neighbor. By illuminating Plato’s epistemological argument for cultural diversity, Plato’s Caves challenges readers to examine themselves and to reinvigorate their love of learning.