This new edition provides a thorough reappraisal of one of the most remarkable and controversial sections of the Republic. Book 5’s radical proposals for the ideal state include an argument for the essential equality of the sexes; provision for full female participation in the work of the Guardians (including warfare); the abolition of the family for this same ruling class, with a sexual as well as economic system of communism; and a policy of eugenic control. Plato feared that some of this material would arouse amusement in his readers; in fact, parts of Book 5 have been subsequently used to support a charge of totalitarianism against Plato, while other elements have led to description of him as the first feminist. Book 5 also examines the relation between knowledge and belief, and in doing so embarks on the great structure of metaphysical thought which forms the centre-piece of the entire work. All these topics receive fresh and detailed consideration in the introduction and commentary, which are designed to make this important work accessible to a wide range of readers.