This study on evidence before international tribunals, with an emphasis on the burden of proof, is considered to be one of the more important and interesting issues of evidence under both municipal and international law. The study is mainly based on documented cases and special attention is paid to the case law of the Iran-United States Claims Tribunal in the Hague.;The study is divided into three parts. Part One presents the preliminary issues concerning the concept of the burden of proof and the burden of evidence, as well as the nature and scope of the burden of proof. Part Two discusses the main aspects of the burden of proof, identified by considering the fact that there are three main actors in each litigated case, viz. the claimant, the respondent and the judge or arbitrator. Different chapters are allocated to: the claimant's role in bearing the main task with respect to the burden of proof; general aspects of collaboration of parties in matters of evidence; and the authority and duties of international tribunals with respect to the burden of proof. Part Two ends with a chapter on the rules of the burden of proof and a discussion on whether or not there are any such rules that could be considered as principles of international law. Some related issues are discussed in Part Three. This work is intended for practitioners of international law and government advisors as well as university professors and students of law.