This chapter examines the impact of Europeanization on member state institutions. Membership in the European Union imposes a variety of constraints and burdens on countries, but it also affords important opportunities and makes available significant resources. Integration initially reinforced the decline of national legislatures, but they have fought back in the last decade. National courts have assumed new functions and become part of a wider Community of law. At the same, the precise effects of the EU have varied cross-nationally as the demands of membership have interacted with differing constitutional arrangements, legal traditions, and political cultures. Moreover, national institutions such as governments, parliaments, and courts have left their mark on the EU and determine to a large extent the capacities of the Union as a system. The chapter considers how EU membership has affected national governments, national parliaments, and national courts.