What is the nature of law? Does our obligation to obey the law extend to unjust laws? From what source do lawmakers derive legitimate authority? What principles should guide us in the design of political institutions? These essays by prominent contemporary philosophers explore how these questions were addressed by ancient political thinkers. Classical theories of human nature and their implications for political theory are examined, as is the meaning of freedom and coercion in Plato's thought and his idea that philosophers should be political rulers. Other essays ask what we can learn from ancient thinkers like Aristotle about the principles of constitutional design or the limits of political obligation.