The move toward a system of integrated administration in the EU poses considerable legal challenges. These arise from the transformation of the EU legal system in all its policy areas. Decreasing separation of the EU from the Member States has given way to multiple forms of co-operation of European and national administrations in the delivery of EU and EC policies. This book addresses the legal challenges of this new level of integration. It explores ways through which accountability, legality, legitimacy and efficiency of the actors involved in co-operative EU administrative action can be ensured. In short, this volume is an essential contribution to the fast evolving area of EU administrative law.