This study considers how and whether EU membership shapes voting behaviour in national elections. It starts by surveying claims about the relationship between EP elections and national elections. Because voters use EP elections as markers for the electoral prospects of national governing parties, the later an EP election follows a national general election, the greater the impact of the EP election on the governing parties' fortunes in the subsequent national election. It goes on to explore whether and how issues of European integration have influenced voting behaviour in national elections. Building on previous studies, the discussion shows that for most of the EU member states, voters' support for EU membership provides the basis for a new electoral cleavage. However, a variety of questions remains to be addressed regarding the extent and character of this electoral cleavage and how this cleavage may develop with further economic integration. The analysis consequently develops a research agenda and several theoretical hypotheses about how the link between macroeconomic performance and support for governing parties may change as economic integration deepens.