This book takes a close look inside political parties, bringing together the findings of an international team of leading scholars. Building on a unique set of cross-national data on party organizations, the contributors set out to explain how parties organize, how they have changed and how they have adapted to the changing political and organizational circumstances in which they find themselves. The contributors are recognized authorities on the party systems of their countries, and have all been involved in gathering data on party membership, party finance and the internal structure of power. They add to the analysis of these original data an expert knowledge of the wider political patterns in their countries, and thus provide insight into the development of parties and party systems from the perspective of party organizations themselves. How Parties Organize offers the most systematic and comparable analysis of party organization in contemporary Europe and the United States.