This article reviews the by now extensive literature on the Europeanisation of the political systems of the EU-15, with an emphasis on parliaments and executives (i.e., governments and ministerial administrations). The Living Review highlights apparently contradictory effects of integration: de-parlamentarisation re-parlamentarisation; bureaucratisation politicisation; and centralisation diffusion. These diverging assessments of the effects of integration do, in part, reflect diversity in the EU-15; in part, they are, however, also a result of differences in the specification of variables, research designs and theoretical approaches. Work that inquires into patterns of Europeanisation - across institutional domains, countries, regions and time - and which seeks to tackle the `methodological nationalism' of the Europeanisation literature promises a clearer picture of the institutional consequences of European integration than we possess at present.