This chapter offers a reconstruction of Aristotle’s theory of humor, both descriptive and normative. First, I offer a reconstruction of how Aristotle would have responded to Plato’s views on laughter. Second, I show that the idea of incongruity is central to understanding what makes a word or an expression funny or humorous. Third, I attempt to reconstruct this theory from a normative point of view (relying above all on the chapter of the Nicomachean Ethics dedicated to the virtue of the “sense of humor”), with the central question “What is a good joke.”