Martha Nussbaum’s new book, The Cosmopolitan Tradition: A Noble but Flawed Ideal, explores the idea of a ‘citizen of the world.’ First articulated by Greek Cynic Diogenes, this perspective prioritized a moral approach to ethics and highlights the equal worth of all humans, rather than association by nation, class, gender, or race. Nussbaum calls this idea “noble, but flawed” and explores the concept from ancient Greece, to Rome, and through the present day. How can the cosmopolitan ideal be updated to include essential shortcomings such as material aid, mass migrations, and the concern we owe to animals and the environment?