One of the fundamental objectives of international investment agreements (IIAs) is to protect the rights and interests of foreign investors in the territory of a contracting State. Why, then, have tribunals often exercised jurisdiction ratione personae over the claims of dual nationals against their own State? The answer lies in the silence of IIAs on the matter of dual nationals. Such agreements have failed expressly to mention dual nationals in their definitions of 'investor' or 'national', which has created lacunae that are open to interpretation. Tribunals have often fallen back on international law to fill these gaps and accurately to determine the nationality of an investor's claims. They have taken into consideration the text of the IIAs, the text of institutional rules and the general principles of international law. The principle of 'dominant and effective nationality', as propounded in the Nottebohm case, has made frequent appearances in such interpretation processes. However, the application of this principle has been inconsistent over time, with different tribunals taking different stances. In this article, the author traces this varied approaches of tribunals. In doing so, he analyses the text of and the awards delivered in disputes arising out of the Algiers Declaration, the North American Free Trade Agreement (NAFTA), the United States-Mexico-Canada Agreement (USMCA), the Convention on the Settlement of Investment Disputes between States and Nationals of Other States (ICSID Convention), the Dominican Republic-Central America Free Trade Agreement (DR-CAFTA), the United Nations Commission on International Trade Law (UNCITRAL) Arbitration Rules and various bilateral investment treaties (BITs). Based on this analysis, the author proposes several changes that States should consider in the future negotiation of BITs to restrict a claim by a dual national against its State of nationality.
