Despite the importance of second chambers to the success of constitutional democracies around the world, today many fundamental questions about bicameralism remain understudied and undertheorized. What makes bicameral reform so difficult? Why choose bicameralism over unicameralism? What are the constitutional values of bicameralism? This innovative book addresses these questions and many more from comparative, doctrinal, empirical, historical and theoretical perspectives. Featuring contributions from leading and emerging scholars in the field, this book provides a timely account of the tensions between bicameralism and its reform, demonstrating for the first time how this relates to the protection of liberal democracy and the rule of law. Contributors analyse the pressures that contemporary constitutional politics exert on bicameralism in an array of countries and legal systems, including the complex relationships between the EU and national second chambers. Scholars and students of comparative and constitutional law, legislative studies and political science will find this book an invaluable resource. Policymakers at national and EU levels, parliamentarians and others working closely with parliamentary institutions will also find it insightful.