The International Investment Arbitrator’s Duty to Apply the Law.

This article explores the sources, nature, and implications of an arbitrator’s duty to decide according to the governing law in investor-state arbitrations. It advances a contractarian conception of arbitral authority in investor-state arbitration, whereby the agreement of the states parties to the investment treaty is the source of both the arbitrator’s power to make decisions and the primary constraint on that power: the duty to apply the law. It argues that the choice of law provisions in investment treaties have a constitutional character for arbitral tribunals, such that a failure to apply the chosen law constitutes an excess of the tribunal’s powers which, if manifest, justifies annulment or non-enforcement of the award. The article concludes by considering the implications of this contractarian theory of arbitral powers and duties for arbitrators, disputing parties, and states seeking to reassert control over the investor-state dispute settlement system. [ABSTRACT FROM AUTHOR]