This chapter explores the odd logic of interest group membership. People join interest groups for different reasons, and these reasons can shape the structure of a group and the kinds of political goals it fights for. A fledgling group needs a major infusion of start-up capital from some type of patron to create and sustain it through those critical first years of collective action. Political scientist David Truman built a theory of politics and government around the assumption that society is a plurality of groups and that each of these groups are composed of people who share interests. Some groups serve small, tightly defined social or economic interests. Truman said that the size of the group community reflects the number and distribution of political threats to formerly latent social interests across the country. American Automobile Association is a political organization that maintains a large office in Washington, where its staff lobbies for greater highway funding and other pro-car policies.