As Steenbergen and Marks (Introduction) argue, the definition and substantive content of the political space is crucial for understanding the nature of political competition in the European Union. In the study of industrialized democracies, including the EU member states, scholars often define the policy space in terms of voter preferences over policy (see Gabel and Huber 2000). Since parties and representatives compete before an electorate, the ideological structure of voters' preferences is fundamental to understanding political contestation. Consequently, one common approach to defining the political space is empirically to examine how an electorate structures its policy preferences.

In this chapter, we attempt to describe the EU policy space in the same manner: by examining the structure (or lack thereof) of EU citizens' preferences over EU policy. However, it is important to note that voter preferences do not play exactly the same role in EU politics as in representative democracies. For one, the links between policy-makers and citizens are different in the European Union than in a typical representative democracy. The Council of Ministers – arguably the most important legislative body in the EU – consists of representatives of national governments elected in national, not EU, elections. It is relatively uncommon that national governments fall or lose elections due to their positions taken in the Council of Ministers. As a result, past research has, at least implicitly, dismissed the EU electorate as a salient constituent for these national representatives.