European Union (EU) governance faces a fundamental implementation and enforcement dilemma. On the one hand, calls for effective EU policies are manifold and have increased over time. On the other hand, the competence to implement and directly enforce EU policies remains with the member states. To overcome this dilemma, an emerging institutional architecture is taking form in which European Administrative Networks (EANs) and agencies assist the Commission in improving the implementation and enforcement of shared policies. This special issue provides a state-of-the-art analysis of EANs and related agencies as core components of the structure in making. To set the scene, this introduction presents different accounts of the establishment and development of EANs in relation to agencies. It then presents a functional continuum of EANs, spanning from information-sharing, data exchange to problem-solving networks. Finally, we discuss the challenges and shortcomings of the emerging, yet still diffuse, institutional architecture, including its accountability.