The administration of the traditional nation-state used to operate as a rather closed system to the outside world. Today, cooperation between the public authorities of different States and between States and international bodies is a common phenomenon. Yet the characteristics and mechanics of such cooperation can hardly be understood using the concepts domestic public law or public international law currently on offer. Conventional concepts, such as federalism, confederalism or State-centered “realism” hardly fathom the complexity of interactions or reflect the changed role of the State, while more recent concepts, such as multi-level systems or networks, seem to encompass only parts of the phenomena at hand. Given this void, we propose to explore the notion of “composite administration” (Verbundverwaltung) and argue that it offers a concept which can combine more coherently the seemingly diverging legal elements of cooperation and hierarchy that distinguish administrative action in what often is called a multi-level administrative system. Even though the concept of composite administration was originally designed and further developed with respect to the largely federal European administrative space, we suggest testing the concept in the wider context of international cooperation. We believe that it offers valuable insights and raises critical questions, even though we do not intend to insinuate any proto-federal prospects of the institutions discussed in this paper.