George Tsebelis' veto players approach has become a prominent theory to analyze various research questions in political science. Studies that apply veto player theory deal with the impact of institutions and partisan preferences of legislative activity and policy outcomes. It is used to measure the degree of policy change and, thus, reform capacity in national and international political systems. This volume contains the analysis of leading scholars in the field on these topics and more recent developments regarding theoretical and empirical progress in the area of political reform-making. The contributions come from research areas of political science where veto player theory plays a significant role, including, positive political theory, legislative behavior and legislative decision-making in national and supra-national political systems, policy making and government formation. The contributors to this book add to the current scholarly and public debate on the role of veto players, making it of interest to scholars in political science and policy studies as well as policymakers worldwide.