In this book, Carol Mershon and Olga Shvetsova explore one of the central questions in democratic politics: how much autonomy do elected politicians have to shape and reshape the party system on their own, without the direct involvement of voters in elections? Mershon and Shvetsova's theory focuses on the choices of party membership made by legislators while serving in office. It identifies the inducements and impediments to legislators' changes of partisan affiliation, and integrates strategic and institutional approaches to the study of parties and party systems. With empirical analyses comparing nine countries that differ in electoral laws, territorial governance and executive-legislative relations, Mershon and Shvetsova find that strategic incumbents have the capacity to reconfigure the party system as established in elections. Representatives are motivated to bring about change by opportunities arising during the parliamentary term, and are deterred from doing so by the elemental democratic practice of elections.

‘Future scholars will be much more careful to treat political parties as endogenous coalitions of legislators and party system dynamics as the evolution of these coalitions. Mershon and Shvetsova offer an excellent starting point for this discussion. It is also very welcome to find a well-crafted new book blending theory and empirics in the best traditions of modern comparative politics.’

Michael Laver - New York University

‘What happens between elections during the life of a parliament when politicians engage in career calculations with potential policy implications? Party switching may only occasionally have broad impact in congressional-style legislatures, but in multiparty parliaments, as Mershon and Shvetsova so compellingly show in this new book, such machinations can shift policy, undo governments, and realign coalitions. The authors provide a compelling theoretical argument, rich case studies, and systematic quantitative evidence, shining a bright light on this important topic.’

Kenneth A. Shepsle - George Markham Professor of Government, Harvard University