ITLOS and the importance of (getting) external rules (right) in interpreting UNCLOS

The Advisory Opinion handed down by the International Tribunal for the Law of the Sea (ITLOS) on 21 May 2024 is truly remarkable. However, while ITLOS succeeded in noting the relevance of many other treaties and customary norms in international law, it fell short of a comprehensive and consistent approach to determining which other treaty norms would be relevant to the interpretation of UNCLOS and how. Establishing coherence by “taking into account external rules” means more than a general reference or a pick-and-choose approach to some relevant norms in an external treaty, while not to others.