Political parties have been studied as organizations for more than a century. Over time the focus of party research has shifted, from normative concerns with organizational democracy to the comparative analysis of organizational evolution and party functions. In this article we document the trajectory of party organization research, analyzing the value of the comparative method and evaluating the predictive power of research in our field to consider how it may add value to the study of other types of organizations. We focus on four established fields: party leadership, candidate selection, party membership and party regulation, but also present some of the newest and most promising research themes in the field, including personalization, evolving forms of participation and affiliation, and the relationship between political parties as organizations and social movements.