Abstract
Joint Interpretative Statements have grown in popularity in recent years as a tool States can use to authoritatively interpret, or reinterpret, investment treaties with the seminal case being NAFTA but provisions for making them have been included in numerous investment treaties and India, Colombia, France, Mauritius, and the EU member States themselves have recently entered into joint interpretative statements. The CETA Joint Committee would also appear to be close to issuing its first "decision" which, in effect, is a joint interpretative statement. Despite this growth, in general, investment tribunals are ill-equipped to apply such statements and, as case studies analyzed in the article show, often commit serious errors when deciding cases involving them. These errors include not applying the relevant articles of the Vienna Convention on the Law of Treaties (VCLT), failing to consider decisions by international tribunals, including the ICJ, regarding joint interpretative statements, and ignoring "the teachings of the most highly qualified publicists" with respect to such statements. These failings risk undermining States' legitimate use of joint interpretative statements, as well as eroding the legitimacy of the ISDS system as a whole, due to repeated misinterpretations and misstatements of the applicable law. This paper aims to respond to the crisis by firstly setting out the relevant international law principles, with these being found primarily in the VCLT, secondly outlining when and how tribunals, and on occasion State courts, have fallen short in their analysis of said principles, and thirdly outlining various possible "futures" for joint interpretative statements, as well as suggesting means by which States might ensure that they are properly applied.