Introduction

As early as 1958, Ernst Haas considered political parties as being essential actors of European integration and regarded their responses as indicators for the progress of the European project. Recent developments in the course of the integration process cast doubts over the ensuing relevance of Haas’s assumptions. European integration has introduced patterns of governance that fit uneasily into traditional models of party government. Partisan channels of representation and parties’ influences on policy outcomes are fundamentally weaker in the European polity than in the domestic arena. Joint decision-making, transfers of competence to non-majoritarian institutions and self-imposed policy constraints have drastically narrowed the policy space of national party competition by enfeebling parties’ abilities to compete over clearly distinguishable policy platforms. European integration has furthermore strengthened non-partisan channels of representation by institutionalising alternative sources of policy input. What follows from these preliminary observations is that party government is not featured among the main organisational principles of the European polity. One could thus reasonably qualify a study devoted to the impact of European integration on domestic party politics as an anachronistic enterprise. However, despite the limitations imposed on national political agency through European integration, political parties are still relevant actors in the European polity. Parties play a key role as the central recruiting instances for the European Parliament, the Council of Ministers and the European Council. Moreover, studies have shown that national party affiliation affects the selection of European Commissioners (Döring 2007; Wonka 2007). With the enhanced power of the European Parliament in the EU’s institutional architecture, political parties have come to play an ever-growing role in European policy-making beyond the level of national executives. Political groups in the European Parliament constitute the primary locus of party politics at the European level (Schmitt and Thomassen 1999; Hix and Lord 1997). Their main function is to solve a collective action problem by ensuring coordination between legislators with similar policy preferences. Political groups have become the main variable for explaining voting behaviour in the EP (Hix et al. 2007) and are thus central actors in shaping European policy outcomes. Most importantly, however, national political parties play a central role in establishing the patterns of national competition over European integration. They remain the key players that are able to determine how and, most crucially, if European integration is translated into national political debates.