This article tries to provide a dynamic interest group theory. Using the economic method of the 'homo economicus' demand for and supply of policy catering to the needs of pressure groups are analysed. Central are the notions of information and organisation costs that face latent groups treatened by already existing groups. These notions permit to integrate the existing theories on pressure group into one global dynamic theory. The economists' rent seeking theory and the political scientists' pluralism and neo-corporatism can thus be understood as stages in a continuing process.