This project explores different frames for understanding the investment treaty system and what these mean when it comes to resolving a variety of contentious issues. Investment treaties are clearly creatures of public international law: they are entered into by two or more states and are substantively governed by public international law. However, they are distinct from most public international law treaties because the vast majority of them permit investors to bring arbitral claims directly against host states based on procedural rules and enforcement mechanisms developed largely in the context of international commercial arbitration and investor–state contracts. Accordingly, the system grafts private international law dispute resolution mechanisms onto public international law treaties.

Comparisons are also drawn between the investment treaty system and other subfields of public international law that concern a state’s right to act and regulate domestically, like trade and human rights, which Anthea groups together as examples of ‘international public law’. Like international trade law, investment treaties are international economic law agreements that require a delicate balancing between economic and noneconomic interests. And like certain international human rights’ regimes, investment treaties are interstate agreements that regulate a state’s treatment of non-state actors within its territory and permit those actors to challenge governmental conduct before an international body.

Why are these comparisons important? Investment treaties have traditionally been short and vaguely worded, while the system as a whole is new and under-theorised. On a micro level, participants routinely draw on comparisons with other legal fields when seeking to fill gaps, resolve ambiguities, or understand the system’s nature. On a macro level, this ‘clash of paradigms’ appears in competing conceptualisations of the investment treaty system as a subfield within public international law, as a species of international arbitration, or as a form of internationalised judicial review. These distinct frameworks help to shape understandings of the investment treaty system’s nature and its development by emphasising certain features, and empowering particular actors, over others.