One of the main ways of understanding politics inside legislative institutions is to investigate the shape of the policy space. The number of policy dimensions and the location of actors on these dimensions determine, among other things, which actors are pivotal and the possibility and direction of policy change (e.g. Tsebelis, 2002). Not surprisingly, a fast growing area of political science research in recent years has been the estimation of actors' ideal points. This has taken a variety of forms and methods, such as scaling of roll-call voting data (e.g. Poole and Rosenthal, 1997), hand coding of party manifestos (Budge et al., 2001), surveys of experts' opinions of parties' positions (e.g. Laver and Hunt, 1992), or computer coding of political statements (e.g. Laver et al., 2003).

The European Parliament is an especially interesting object for spatial analysis of the dimensionality of politics because of its unique features. There is considerable heterogeneity between the cultures, histories, economic conditions and national institutions of the EU member states. Therefore, politics in the European Parliament is likely to be more complex than politics in many national parliaments. MEPs are also members of national parties as well as European political groups. A legislature with such characteristics is potentially one with high dimensionality.

In this chapter we describe the policy space inside the European Parliament by applying an established scaling method to the roll-call votes between 1979 and 2004.