Arbitrators are the lightning rod for investment arbitration’s most contentious political debates. Investment arbitration was originally conceived as a means to depoliticize international investment law. The regime was designed to extricate investment disputes from national courts and gunboat diplomacy, entrusting them instead to a neutral law-bound process. According to its critics, however, investment arbitration is neither a neutral, nor a legitimate law-bound process. They lay most of the blame with international arbitrators. Critics contend that, instead of law and appropriate policy considerations, investment arbitrators’ decisions are often the product of extra-legal factors — from their own ideology, to the nature of disputants, to their personal self-interest For every hypothesis about what extra-legal factors affect investment arbitrators’ decisions, there seems to be an equal and opposite hypothesis. The purpose of this paper is to examine the state of empirical research about investment arbitrators as a tool for developing a more comprehensive understanding of international adjudication. Through the lens of specific reform proposals that draw from empirical studies in the field, it analyzes the limitations and potential contributions of empirical research to the development of investment arbitration. Part I of this paper examines some of the methodological challenges raised by empirical research that seeks to prove or disprove these claims about investment arbitrators. Part II offers an evaluation of selected reforms that have been proposed for investment arbitration based, in part, on some findings in empirical research. In Section A, I examine Albert van den Berg’s study of dissenting opinions by party-appointed arbitrators, and related proposals to dramatically reduce if not eliminate dissenting opinions. Section B examines Gus Van Harten’s study of jurisdictional rulings, and related proposal for a permanent International Investment Court. Part III examines the risks of allowing substantive policy preferences to affect empirical analysis, and argues for integration of research about investment arbitrators into a comprehensive theory of international adjudication as a neutral and law-bound process. To that end, it proposes that future research be integrated into comparative institutional analysis with other forms of public international adjudication to develop a more comprehensive theory of international adjudication.