This book examines the legal regime of direct evidence before international jurisdictions, distinguishing between interstate and arbitral mechanisms. It highlights the central role of direct evidence in international litigation as an instrument of demonstration, conviction and legitimization of legal claims. The study begins by defining the essential concepts and analyzing the different forms of direct evidence, in particular documentary and testimonial evidence, taking into account comparative legal traditions. Secondly, it examines the rules applicable to the administration of evidence, whether in state or arbitral jurisdictions, with particular attention paid to IBA and OHADA standards. The analysis highlights the evolution towards a cooperative model based on procedural fairness and the active participation of the judge.The book concludes with the need to strike a balance between evidentiary freedom and legal certainty, as a guarantee of fair and efficient international justice.