For much of the last century, global actors have sparred over the international legal rules governing the compensation a state should pay a foreign investor when it expropriates the latter's property. The competing claims have had many dimensions, including the content of customary international law and the line between bona fide regulations and expropriations. In the modern age of international investment agreements (IIAs), a debate continues over another key issue: When a state expropriates a

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... foreign investment in violation of an IIA, where should a tribunal look for the standard of compensation—to the amount the treaty requires the state to pay when it expropriates, or to an external standard for violations of international law generally? Each is alluring to a tribunal for its legal visibility—one spelled out in the very text under examination, and one stemming from a venerable international court case. But they may point to significantly different results for the investor and the host state. And investor-state tribunals remain wildly inconsistent, even incoherent, in their choice and use of those standards. It remains a significant source of disagreement in contemporary investor-state arbitration.