Scholars of political thought often view Plato as a ‘political moralist’, or a ‘utopian’ partly due to the Republic’s emphasis on ‘justice’. But in the Republic, Plato offers a distinctive theory of legitimacy, one that grounds legitimacy on an interdependent relationship between justice and moderation. Justice requires that the principle of specialisation be respected, while moderation requires that citizens agree about who should rule. But citizens will only agree if their ‘necessary’ desires are satisfied. Conversely, the ‘necessary’ desires can only (...) be satisfied when the principle of specialisation is maintained. In this way, justice requires moderation, and moderation requires justice, and both are necessary for legitimacy. Plato’s theory of legitimacy is positioned in relation to existing accounts, especially those of John Rawls and Bernard Williams. It is shown that Plato’s theory is a genuine theory of legitimacy, not a theory of acquiescence. In the concluding section, Rawls’ theory is subjected to a critique based on Plato’s theory. (shrink)