In the context of increasing polarization over European integration in the period following the financial crisis, we contrast two forms that polarization might take: mainstream polarization in which the issue of integration is increasingly integrated within existing party cleavages and party systems; and extreme polarization with potentially destabilizing political consequences for party systems. To address these issues, we employ two expert surveys conducted in 2007/8 and 2013 in 24 European democracies. We find that extreme parties adopt even clearer anti-EU positions in 2013 than they did in 2008 while mainstream parties have modified their pro-integration positions hardly at all. However, we also find that extreme polarization is more clearly found in Western Europe where European integration issues have been less integrated into the main lines of party competition than in the East.
