Plato’s Republic covers a very wide range of philosophical topics, many of them also addressed in other Platonic dialogues. The papers in this volume, arising from the Institute of Classical Studies research seminar in ancient philosophy in 2007-2008, illustrate the range and diversity of responses to the Republic in antiquity. These responses show, for example, how in criticizing the doctrine of the tripartite soul Aristotle is as much concerned with the Timaeus as with the Republic, how Cicero regarded the Republic and the Laws as complementing one another, and how Proclus treated the discussion of music in the Republic alongside the account of cosmic music in the Timaeus. Other papers examine the interpretations of the myth of Er offered by the Middle Platonist Alcinous and by Porphyry, and Proclus’ place in the ancient reception of the Republic.