Rules of evidence may vary significantly from one legal system to another. Yet, the issue of the law applicable to evidence remains an uncertain and relatively unexplored area in private international law. The issue is not straightforward : evidence is at the boundary of a traditional distinction in private international law between the procedure, which logically comes under the lex fori, and the merits, which are subject to conflict of laws and the lex causae. On this issue, opinions are divided in comparative law: common law countries tend to classify evidence within the category of “procedure”, whereas civil law countries may treat it more as a matter of substantive law. Moreover, within the same legal system, the approaches adopted in this respect lead in reality to a certain fragmentation of the law applicable to evidence, even though the various issues relating to evidence (subject of evidence, burden of proof, admissibility of methods of proof, probative value of admitted methods, standard of proof, evaluation of evidence) are clearly interrelated. This fragmentation is undoubtedly unfortunate. One might argue that in international arbitration these difficulties are exacerbated for several reasons. First, since arbitrators do not have a forum, they do not have, unlike State courts, a system of solutions by which they would be bound, and which would guide them as for this division between procedural and substantive law. Secondly, national arbitration laws contain very few rules of evidence specific to arbitral proceedings that could offer guidance to the arbitrator. Moreover, the general rules of domestic procedural law are generally not binding in arbitration. The arbitrator may therefore find himself at a loss when it comes to determining solutions in this respect. On the other hand, the arbitrator is not hindered by the burden of the domestic approaches and is ultimately put in a privileged position to adopt more rational, less disparate solutions, essentially dictated by efficiency and predictability for the parties. In particular, the arbitrator may wish to favor an approach, specific to international arbitration, which would come outside the conflict of laws scope and would be more unitary and predictable. In this respect, there is indeed a significant reduction in conflict of laws to deal with evidence in international arbitration in favor of uniformity of practice. Nevertheless, conflict of laws persists to a significant degree. In this context, some conflicts are easily resolved, while others prove to be more problematic. However, the issue is not unsolvable, as long as one is more interested in the substance of the question raised than in the procedural dimension of evidence.