This study deals with changing conflict structures in West European societies and their mobilization by political parties. In general, there are two basic approaches to handling such a question: the first one concentrates on the changing relationships between political actors and often resorts to concepts of network analysis (Laumann and Knoke 1987; Laumann and Pappi 1976; Knoke et al. 1996; Scott 2000; Wassermann and Faust 1999). In this book, we follow the second approach and analyze issue-positions of parties as well as of voters, since we are especially interested in the thematic basis of political conflicts. This is not only the standard approach in political science (e.g. Kitschelt 1994, 1995) but has recently become even more important because of the growing significance of issue-based voting behaviour (Downs 1957; Key 1966; Budge and Farlie 1983a; Franklin 1985; Aardal and van Wijnen 2005). We expect the parties, the main political actors in West European democracies, to select the issues they articulate in party competition as well as their positions strategically. But we also look at the other side of this competition where we are interested in the changing issue-positions of the voters. However, contrary to pure rational choice or individualistic approaches, we combine the issue-based approach with a structural perspective which is focused on the political attitudes of groups. According to our point of view, membership in social groups still constitutes an important basis for the development of issue-preferences.