International investment law is one of the fastest growing areas of international law. It has led to the signing of thousands of agreements, mostly in the form of investment contracts and bilateral investment treaties. Also, in the last two decades, there has been an exponential growth in the number of disputes being resolved by investment arbitration tribunals. Yet the legal principles at the basis of international investment law and arbitration remain in a state of flux. Perhaps the best illustration of this phenomenon is the wide disagreement among investment tribunals on some of the core...