Summary of doctoral thesis: My thesis investigates the role that laughter (gelōs) plays in the good life for Plato and Aristotle. It proposes that, for both philosophers, how one laughs, what one laughs at, and who one laughs with serve as powerful indicators of the health of an agent’s soul. Plato explicitly theorises about laughter in the Republic (388a-389a, 605c-607a), the Philebus (47e-50b), and the Laws (816d-817a, 935a-936a). I argue that, although Plato’s ‘theories’ of laughter are mostly concerned with morally harmful laughter, he also allows for a ‘correct’ form of laughter which is morally beneficial. In the second part of this thesis, I examine Aristotle’s views on laughter in the Nicomachean Ethics, Eudemian Ethics, Politics, Poetics, and Rhetoric. By comparing the two philosophers’ views, I argue that, while laughter is of instrumental value to the agent for Plato, it is both instrumentally and intrinsically valuable to the agent for Aristotle. By taking a comparative approach, my thesis not only explores what we can learn about laughter, comedy and the good life from Plato and Aristotle but also what we can learn about the differences and similarities in their moral psychologies, ethics, politics, and aesthetics when we take their attitudes towards laughter seriously.