This article connects the insights of post-realist scholarship about radical indeterminacy and its consequences for the legitimacy of adjudication to the current legitimacy crisis of the international investment regime. In the past few years, numerous studies have exposed serious shortcomings in investment law and arbitration including procedural problems and the substantive asymmetry of the rights protected. These criticisms have prompted a broad consensus in favor of amending the international investment regime and multiple reform proposals have appeared that appeal to the (...) rule of law ideal as an instrument for increasing the acceptability of the international investment system. This article argues that the reliance of such proposals on jurisprudential approaches that fail to adequately accommodate the post-realist indeterminacy critique and take seriously the role of ideology in adjudication renders reform efforts unable to solve the legitimacy problems of the investment regime. The conclusions suggest the need to abandon implausible claims to depoliticization and face the methodological challenges posed by the promise of ideologically balanced assessments advanced by some rule of law theorists. The article finally points at the urgency to reform traditional approaches to doctrinal work in order to increase awareness of critical challenges and open up doctrinal methods to alternative methodological avenues. (shrink)