The increasing importance of new actors and instruments to conduct internationally relevant behaviour is one of the central elements in the modem international system. This development, which is first of all a sociological phenomenon, has also important legal consequences. Some of these consequences can be seen with regard to the doctrine of the sources of law in public international law. Even though non-legal instruments have always shaped the international system, the number of these instruments is increasing today. Relevant examples concern the broader fields of customary international law and of treaty law. These developments lead to the conclusion that the international system knows “law without sources of law”. The rationale for such a development is rooted in the increasing necessity for the international community of an adequate protection and distribution of global public goods. Thus, “law without sources of law” is not to be seen as a merely negative phenomenon. From a legal perspective, however, it is necessary to give up a positivistic point of view while analysing legal developments in the international system.