The importance of administration in the EU has been growing progressively together with the development of EU competences and tasks in the internal market. From the original model of a Community leaving enforcement with the Member States, the EU has become a complex legal order where administrative tasks are spread among different actors, including EU institutions, EU agencies and national administrations. Within this complex administrative law landscape, agencies and their powers have been essentially ''upgraded''. This volume asks whether any such ''upgrade'' is compatible with EU law and its principles. Exploring both the case law of the CJEU and the regulation relating to EU agencies, the volume asks a crucial question about the legitimacy of the ever-increasing role of agencies in the enforcement of EU law.