Electoral systems are sets of formal rules that create incentives for strategic behavior on the part of voters, (pre-) candidates, party elites, and elected representatives, including legislators and their chamber leaders. Most simply, they translate the choices made by voters into seats won by candidates and parties. In the process, rules influence both how many and which parties are viable and how elected official will go about their time in office as representatives. All electoral systems share a common set of component rules and each rule can take on a number of different values. When combining the values taken by these rules into a system, the number of possible combinations is quite large, which means that specific systems have the potential to provide precise, targeted incentives that govern relationships between political parties - interparty politics - and within parties - intraparty politics. Using novel computational tools and a comprehensive and updated dataset on electoral systems, this book develops precise and transparent measures of both electoral systems' interparty and intraparty incentives. These two simple quantities capture the extent to which a given system encourages the election of a limited number of large parties or a larger number of relatively smaller ones and the extent to which the lawmaking process will be conducted by unified, programmatic parties or by individually noteworthy politicians. They thus allow scholars to test the extent to which electoral rules shape political outcomes about which we care, and they allow practitioners to select the electoral system that is likely to encourage the form of representation they desire. The book shows that these indicators of electoral system incentives can explain variation in interparty politics - the effective number of parties, parties' locations in the policy space, congruence between citizens' preferences and policy - and intraparty politics - the content of campaigns, the amount of constituency service provided, the shape of legislative institutions, levels of party discipline, and the balance struck between programmatic policy and pork barrel politics. Comparative Politics is a series for researchers, teachers, and students of political science that deals with contemporary government and politics. Global in scope, books in the series are characterized by a stress on comparative analysis and strong methodological rigour. The series is published in association with the European Consortium for Political Research. For more information visit: www.ecprnet.eu . The series is edited by Nicole Bolleyer, Chair of Comparative Political Science, Geschwister Scholl Institut, LMU Munich and Jonathan Slapin, Professor of Political Institutions and European Politics, Department of Political Science, University of Zurich.