This paper offers a theory of political parties that places interest groups and activists at its center. This is a departure from standard theories, which have politicians at the center. As we theorize them, parties no longer compete to win elections by giving voters the policies voters want. Rather, as coalitions of intense policy demanders, they have their own agendas and aim to get voters to go along. In a second departure, we take central account of limitations of voter attentiveness, positing an electoral blindspot within which parties can enact whatever policy they wish. Moreover, we posit that parties, as rational actors, do what they can via agenda control, secrecy, and other institutional devices, to keep the electoral blindspot as large as possible. In this way, parties exploit their dvantages in organization to maximize what they can extract from government for their constituent interests. Parties, as we describe them, are an open conspiracy of intense policy demanders against the less active and involved. The paper presents some empirical findings relevant to the theory. The evidence consists mainly of sketches and stylized facts.