How can evolutionary ideas be applied to the study of social and political institutions? Charles Darwin identified the mechanisms of variation, selection and retention. He emphasized that evolutionary change depends on the uniqueness of every individual and its interactions within a population and with its environment. While introducing the contributions to this special issue, we examine some of the ontological positions underlying evolutionary theory, showing why they are appropriate for studying issues in economics, political science and sociology. We consider how these ideas might help us understand both institutional change and the formation of individual preferences.