This third Companion is devoted to ancient theories of language. The chapters range over more than eight hundred years of philosophical enquiry, and provide critical analyses of all the principal accounts of how it is that language can have meaning and how we can come to acquire linguistic understanding. The discussions move from the naturalism examined in Plato's Cratylus to the sophisticated theories of the Hellenistic schools and the work of St Augustine. The relations between thought about language and metaphysics, philosophy of mind and the development of grammar are also explored. The essays will interest those studying ancient philosophy and philosophy of language, the history of thought about language, and linguistics.