The role of international judicial decisions in the development of customary international law

International law is considerably affected by the continuous change and development in the international community and therefore it is a developing branch of law. The participation of new actors to the classical state centric international community causes the enlargement of the international law in terms of its subject matter and this situation particularly necessitates to draw attention to the relationship between existing sources of law and these new actors. The relationship between the international judicial institutions accepted as one of the new actors of international law and customary international law as one of the most controversial and ambiguous sources of international law is a topic to be considered in particular. The questions of what the international judicial institutions with different characteristics understand about customary law, in what way these judicial institutions have positions towards the uncertain characteristic of customary law, to what extent they can apply two element theoretical customary approach, whether they adopt different approaches and methods for the uncertainty of customary law and the difficulty of proving two elements and finally whether all these affect customary law or not are some of the questions that this study seeks an answer. The purpose of focusing on these points in this study is to comprehensively put forward the role of international judicial institutions in the development of customary international law. Accordingly, the activities of international judicial institutions with regard to the determination of the existence of customary international law are touched upon and the effect of international judicial institutions on the content of customary rules is examined. To what extent classical acceptances regarding customary international law within the context of this bidirectional effect of international judicial decisions on customary law are valid in practice will be set forth.