Book excerpt: Describes the development of interest groups in the USA mainly from the 1960s to the 1990s. Using the results of two national surveys of all membership associations operating in Washington in 1980 and 1985, examines the ways in which different types of social groups develop the organizational structures necessary to represent themselves. Describes methods for financing these groups and investigates the strategies they use to influence American politics, including litigation strategies. Considers occupationally based groups in the profit sector and in the nonprofit sector and citizens groups which are open to all. Examines the extent of influence of different groups.