Résumé : This research explores the role of public interest litigants in the circulation of arguments among courts regarding the interpretation of fundamental rights. Such circulation is often labeled ‘judicial dialogue’. ‘Public interest litigants’ are here defined as entities (individuals or groups) with no direct interest in the case, who use procedural avenues to participate in the litigation. Despite extensive scholarly attention for judicial dialogue, the necessity for more empirical research devoted to the exchanges among jurisdictions had been stressed. Three jurisdictions with different postures towards cross-citations were chosen for the analysis: the U.S. Supreme Court, the European Court of Human Rights and the South African Constitutional Court. Among their vast case law, landmark cases were selected dealing firstly with death penalty or related questions and secondly with discrimination on the basis of sexual orientation. Briefs submitted by public interest litigants to courts were collected and analyzed, mainly to inquire about the identity of the actors involved in the cases, to see whether their briefs contain comparative material and, if they do, to record what sort of references are made and whether they are accompanied by justifications supporting their relevance.The analysis reveals that the briefs contain comparative material. Many public interest litigants can be considered as messengers of this information. They push for the detachment of judicial interpretation from the text at hand and propose a variant of the interpretative exercise in which the mobilized material is not exclusively jurisdiction-bound. The cross-analysis also reveals that, contrary to the picture painted by the literature on the phenomenon, there are actually many comparisons in the broad sense (referring for example to a ‘universal practice’) that are used in a norm-centric way, that is, where the simple mention of a comparative element in the form of a broad reference or the outcome of a foreign case should have weight in the adjudication and not in a reason-centric way, that is, by exposing the reasoning of a foreign judge. The research also hypothesized that the comparative material brought by public interest litigants influences the judges. Analyzing the cases using the process-tracing method allowed to substantiate that briefs are read and established that several comparative references brought by public interest litigants were debated during the oral arguments and found an echo in the judgments (in majority and dissenting opinions). Along with the use of other methods such as interviews of judges, the hypothesis was thus confirmed.Exploring the roles of external actors also enables to supply the literature on judicial dialogue with factual insights regarding the identities of the actors behind the circulation of legal arguments. It was found that, in the United States, the traditional domestic ‘repeat players’ (that is, actors often involved in the litigation) do not clearly embrace a comparative approach while most public interest litigants in Europe and South Africa do. Similarly, the pregnant role of transnational actors is underlined. The analysis suggests an explanation drawn from an aspect of the legal culture in which the public interest litigants evolve and which influences their argumentative strategies: the horizon of the ambient rights discourse: a civil rights discourse, more territorially bounded (and more often found in the U.S. context), is distinguished from a human rights or fundamental rights discourse which entails a more cosmopolitan dimension.The final part of the research explores and discusses the justifications provided by public interest litigants to support the relevance of a comparative approach in the interpretation of rights. The compilation of these justifications allows to confront those provided first hand to the judges with those constructed post facto by the scholarly literature. It reveals the uncertain implications of some of these justifications, in particular the one pointing to the universal nature of the discussed rights and the one invoking the need for consistency among the approaches of jurisdictions.The research thus allows to confirm the hypothesis that public interest litigants play a key role in judicial dialogue. Moreover, it points at further promising researches, and this thesis hopes to draw the attention to often neglected elements, such as the identity and status of the actors bringing comparative information, the forms of citations and the roles assigned to them, the aspects of legal culture that are seldom mentioned in the literature and the implications of the justifications explicitly or implicitly provided for the relevance of comparative material.