International investment arbitration has been dubbed the “Antarctica” of international procedural law. This book explores international investment arbitration (IIA) using the searchlight of comparative analysis. Further, it provides answers to several questions, such as the role of ICJ judgments and WTO decisions as a source of inspiration for how proof and the burden of proof are approached in IIA. By investigating various evidence-related issues, the book also sheds light on overarching questions including the role of IIA as a subsystem of international economic law.