The rule of law is a contested and multidimensional concept. In this chapter, the aspects highlighted in the UN Secretary General’s 2004 Report are used as a point of departure, focusing on equal enforcement and independent adjudication of legal rules and principles as well as fairness in the application of the law, legal certainty, the avoidance of arbitrariness and procedural and legal transparency. From such rule of law-perspective, investor-state arbitration will be scrutinized, in particular, in regard to independence and impartiality of arbitrators, what is required for parties to have a ‘fair trial’ before an investment tribunal (procedural fairness, the right to be heard, equality of arms), access to justice given the financial implications for both host states and investors, as well as the adequacy of the ‘control’ system, be it ICSID annulment or set-aside procedures before domestic courts, to guarantee predictable, consistent and legitimate outcomes.