Political science research, especially in recent times, has recognized the centrality of party and executive leaders and their individual characteristics. The attention has been mostly directed towards individual leadership. However, one-chief leadership is not the only existing model of party governance, and some recent developments seem to have put forms of collective leadership into the spotlight. Two parties that have recently achieved remarkable electoral results, the Italian Five Star Movement and the German Alliance 90/The Greens, can be considered examples of alternative models of leadership. This book calls for a deep and systematic analysis of cases of parties in which powers and responsibilities appear to be shared among different individuals rather than being concentrated in the hands of just one leader. Drawing on the literature of organization and management theory, the book fills a gap in the literature of political science by developing a theoretical framework that may provide researchers with the tools for proceeding with the analysis of cases of party collective leadership. To illustrate their approach, the authors have selected three cases - the German Greens, Alternative for Germany, and the Five Star Movement in Italy - that show significant variation across types of collective leadership. The outcome of the empirical analysis contributes to a better knowledge of the nature and functioning of party leadership as well as raises questions that could be further addressed in future research. Donatella Campus is Professor of Political Science at the University of Bergamo, Italy. Niko Switek is DAAD Visiting Assistant Professor at the Henry M. Jackson School for International Studies and the Department of Political Science at the University of Washington, USA. Marco Valbruzzi is Assistant Professor of Political Science at the University of Naples-Federico II, Italy.