A recent revival of interest has taken place in the Epicureans, Stoics and Sceptics, their theories and problems, and the lively debates that went on between them in ancient Greece. This study provides a philosophical introduction to the epistemological and metaphysical debates in which these Hellenistic thinkers marked out for philosophy some of its central concerns. In the first chapter David Sedley introduces the major thinkers of the period in a brief sketch of Hellenistic philosophy. The papers which follow were originally delivered and discussed at an international conference held in 1978 at Oriel College, Oxford, which was the first of a series of Symposia Hellenistica.