Evidentiary norms govern every single aspect and stage of the fact-finding process, fact-finding being one of the three necessary elements to resolve a case (the other two being ascertaining the applicable law and applying the law to the facts). Yet, despite its critical role in the adjudication of disputes before international courts and tribunals, international evidence law remains largely understudied. The present doctoral dissertation is dedicated to the study of the law of evidence in public international law. Taking the WTO dispute settlement as a case-study, the work engages in a quest to systematize the lex lata of international evidence law and to lay the foundation for the emergence of new evidentiary standards and techniques (lege ferenda) in WTO dispute settlement, and, more generally, in international adjudication. The main proposition that this work advances and seeks to demonstrate is that international evidence law can be systematized and expanded through two methods. First, by making use of all the sources of law and evidentiary powers available; and second, by engaging in cross-fertilization with the evidentiary rules and practices of other international adjudicative systems along the route of the evidence. The author applies both of these methods to WTO adjudication. The present doctoral research can be regarded as a continuation of, as well as a confrontation to, Sandifer’s, Kazazi’s, and Amerasinghe’s work in the area of international evidentiary law.