This book offers a systematic exploration of the role of religion and religiosity in electoral politics in Catholic, Protestant, and religiously mixed countries across Western Europe and in the United States. The chapters approach the relationship between religion, religiosity, and electoral behaviour from a variety of different angles. They include analyses of secularization trends; comparative studies of the links between vote choice and religiosity; longitudinal single country studies; and a novel discussion of the theoretical underpinnings of the politicization of religion that provides a radically new framework for the analysis of the role of religiosity in election studies. The volume shows that despite the expectations of secularization theory, religiosity remains relevant when casting votes. It also argues that the traditional notion of religious cleavage should be replaced with the more accurate idea of religious voting. Chapters draw on National Election Studies data and comparative datasets such as European Values Studies (EVS), European Social Surveys (ESS), and European Election Studies (EES) to empirically test expectations regarding religious voting. The results show that variations in religious voting are conditional on both the agency of political and ecclesiastical leaders when politicizing religious issues and the legacies of previous societal and political religious conflicts, regardless of whether the original party system had a predominant religious cleavage.