During the 1980s and 1990s, 16 Latin American countries passed some sort of amnesty law to bar prosecutions against former state officers responsible for perpetrating human rights violations during dictatorships and armed conflicts. Today the situation is very different. Since the early 2000s, judiciaries across the region have become a beacon of progress in the area of transitional justice by fully embracing a set of juridical arguments and doctrines derived from international human rights law that enabled them to take bold jurisprudential steps against impunity. Why did judicial corporations evolve from unresponsive bureaucracies into suitable arenas for the advancement of rights claims? Under what conditions do judicial branches acquire the technical capabilities and the political will to become powerful players in salient political struggles such as those surrounding transitional justice? I argue that the aforementioned sea changes in jurisprudence are not circumstantial adaptations to changes in the political environment, but instead result from internal revolutions within judicial corporations. This transformation involves the deinstitutionalization of formalist and positivist legal cultures, historically protective of conservative interests in Latin America, and the entrenchment of a juridical vision committed to the defense of human rights. Activists and their lawyers succeed in sending criminals to jail when they modify the legal thinking, technical capabilities and political will of judicial corporations. Effective activists contest control over the allegiances of judicial actors by mounting informal pedagogical interventions to familiarize judges and prosecutors with complex and unknown juridical doctrines derived from international human rights law. By promoting the acceptance of these novel arguments, activists make the toppling of impunity dispositions legally possible. Litigants further the process of institutional change by seeking the replacement of judicial actors who staunchly oppose the progress of the lawsuits. In addition to enhancing judges' technical capabilities, these transformations reshape their understanding of their institutional mission, providing judicial actors with cultural resources that facilitate coordinated resistance against soldiers and politicians seeking to put trials on hold. I explore these processes by comparing the cases of Argentina and Peru. Fieldwork in both countries included research in newspaper archives; content analysis of rulings and transcripts of oral trials; participant observation in various courts; interviews with political leaders, victims, human rights lawyers and especially, judges and prosecutors; and original surveys of judicial actors. Using these sources I am able to attribute the success of transitional justice in Peru and Argentina to the aforementioned informal mechanisms of institutional change activated by human rights organizations