Philosophers distinguish two non-exclusive ways of defining a concept. One is ‘by intension’, which is specification of the essential features something must possess in order to fall under the concept. The other is ‘by extension’, which involves giving examples of the range of things that fall under the concept. This latter is Umberto Eco’s method in considering ugliness, a concept rarely discussed in its own right but left to shift for itself as the complement of beauty. What this remarkable book shows is that ugliness is not only no less interesting than beauty, but also no less diverse or culturally significant.