Mixed Disputes in International Dispute Settlement

This report is the result of a 14-month project implemented by BIICL in 2024 and 2025. It examines the settlement of mixed disputes by international courts and tribunals. It provides examples from the practice of international courts and tribunals in the law of the sea and other areas of international law.

Mixed disputes are defined as cases brought before international courts and tribunals involving intertwined legal issues governed by different legal regimes, encompassing both disputes over matters falling within the forum's jurisdiction (internal issues) and disputes implicating rules beyond that jurisdiction (external issues). As a result, disagreements may arise on the scope of a forum's subject-matter jurisdiction. Does the forum lack jurisdiction over the external issue? Can it decide the external issue under certain conditions? Alternatively, does the forum lack jurisdiction over both internal and external elements in a specific mixed dispute?

While the term mixed disputes is particularly prevalent in the law of the sea discourse, the issues in the dispute settlement system under the UN Convention on the Law of the Sea (UNCLOS) have parallels in other fields of international law. Accordingly, the report focuses on mixed disputes in the law of the sea and the tests and techniques used by the relevant courts and tribunals but also looks at practice beyond the law of the sea to infer tenable findings on international dispute settlement more broadly including the approaches of dispute settlement bodies dealing with issues relating to international human rights law, international criminal law and international trade and investment law.

The research team consulted widely with academics and practitioners with knowledge and experience in the settlement of disputes by international courts and tribunals. The scholarship referenced in the report may be consulted for further study of the issues raised by mixed disputes in international law.

The research team extends its thanks to everyone who contributed to this work.

Find out more about BIICL's work on international courts and tribunals here.