Mixed Disputes in International Dispute Settlement

This project explores how international courts and tribunals address 'mixed' disputes, defined as cases involving intertwined legal issues which are based on different legal regimes, encompassing both disputes over rules that fall within the adjudicator's jurisdiction ('internal issues') and disputes implicating external rules ('external issues'). In this situation, the parties may disagree about the applicable scope of jurisdiction ratione materiae, i.e. whether and to what extent the adjudicator's jurisdiction includes external issues potentially falling beyond the treaty framework under which the claims were formulated. These disputes can also be described as having a 'mixed character' or of a 'mixed nature'.

The project 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 wider practice beyond the law of the sea to identify trends, clarify ambiguities, and draw practical conclusions for States, advisors, and courts.

A project report "Mixed Disputes in International Dispute Settlement" was published in December 2025.