The ‘’classical’’ scholars who wrote about political parties—Ostrogorsky, Michels, Weber, Duverger—conceived of them as being above all organizations, arguing that in order to understand and explain their activities and transformations, it was necessary to analyze their organizational core. This perspective was abandoned by later scholars, but in this innovative book, Angelo Panebianco takes it up again, and, with the benefit of recent advances in organizational studies, extends it to offer new insights into the functioning of political parties. Making use of several different social scientific disciplinary traditions, Panebianco develops an original framework for the analysis of political parties. He formulates a wide-ranging theory of the ‘‘organizational development” of parties, paying particular attention to their internal power conflicts, on the basis of which he elaborates a general interpretive scheme for the analysis of party change. He also presents new hypotheses on the relations between parties and their environment, on bureaucratization, and on the role of ideology. He tests these theories through an historical comparative analysis of European political parties, re-examining their history in the light of his theoretical concerns. As a fresh treatment of a central issue in political science, this distinctive and significant contribution to the theory of political parties will appeal widely to political scientists and sociologists, while its extensive and balanced discussion of other works on the subject, albeit in the context of its own argument, make it also a valuable resource for students.