The role of national legislatures in European integration has received much-needed attention in recent years. This interest is primarily explained by the rapid growth in the policy competence of the European Union (EU) and by the realization, in line with the deparliamentarization thesis outlined in this chapter, that parliamentary bodies were, both individually and collectively, becoming increasingly marginalized in the EU policy process. Hence both scholars and politicians began to consider ways of making national MPs more involved in the processing of EU matters. In a broad context parliaments are central institutions in European systems of government. They elect and control the government, approve legislation, and as the bodies responsible for amending the constitution hold the ultimate power in society. Yet such constitutional perspective is arguably increasingly divorced from reality. National parliaments are almost without exception portrayed in the literature as reactive institutions, casting rather modest influence on policy initiatives coming from the executive.