South Centre Report, October 2026
Reclaiming Authority in Investment Arbitration: Joint Interpretations in International Investment Agreements and Investor-State Dispute Settlement
By Adamant Aldo Ruddyard, Diego Flávio Fontoura José, Sidney Tambasi Netya
Supervisor: Prof. Fuad Zarbiyev
Prepared for the South Centre as part of the Geneva Graduate Institute’s LL.M. Legal Clinic Programme, International Economic Law Stream
In order to analyze to what extent joint interpretations of international investment agreements (IIAs) influence the decision-making of arbitration tribunals in investor-State dispute settlement (ISDS), this report will explore the evolving role of joint interpretations in international investment law and their impact on the balance of power between States and arbitral tribunals. The first section examines the shift towards joint interpretations and State control, highlighting key developments in treaty design and the increasing use of joint interpretation clauses (JICs) and how they potentially reshape investment tribunals’ decision-making. The second section delves into the characteristics and benefits of joint interpretations, discussing their effectiveness in addressing ambiguities in investment treaties and their potential outcomes to investment arbitrations. Finally, the report will conclude by offering recommendations for enhancing the role of joint interpretations in the investment arbitration framework. The recommendations will address the challenges States face in ensuring the effective use of these mechanisms, proposing ways to integrate JICs into the broader reform efforts of international investment law.