The widespread possibility to submit amicus curiae briefs in international courts and tribunals is a recent phenomenon. The first purpose of this paper is to verify the alleged Roman origins of amicus curiae, and to trace the emergence of its use in international law. The second and primary purpose of the paper is to assess the fairness of the new procedures, by considering the rules and the case law of several jurisdictions, and evaluating them according to procedural criteria. A set of questions that has been considered deals with the idea of public participation: clarity of the procedures, equality of the treatment of all the interested entities; conditions and reasons for accepting or refusing the proposed amici; emergence in the final decision of the amici submissions, etc. The other set of questions deals with the rights and interests of the parties to the dispute, including the interest in efficient proceedings.