In the last three decades the world has seen an astonishing rise in transnational organized crime, a challenge that made the International Society search for new ways to prosecute organizations that seem to grow more powerful every day. In International Society, each and every State is an independent and sovereign entity, which means that no other State or international entity may meddle in another Stat s internal affairs. This means that the prosecution of transnational crime cannot be entrusted to an international organ, nor can a State pretend to pursue an offender into another s territory. To overcome this barrier, new and faster methods of international cooperation have been adopted with authorities being granted a greater degree of autonomy to perform acts of mutual legal assistance. The same phenomenon is occurring in Brazil, although in a much slower pace. This doctoral dissertation seeks to establish that the Constitution, Brazilian procedural and criminal laws, and the international treaties to which Brazil is party assign to the Ministério Público - MP, as the autonomous government office in charge of criminal prosecution, the task to assist international authorities in prosecuting transnational crime. Specially at the Federal level, the Ministério Público is the main actor in the investigation and judicial prosecution of criminals, however recent decisions reached by the Supremo Tribunal Federal and the Superior Tribunal de Justiça, Brazil s highest courts, have voided acts of direct cooperation by judicial authorities, raising a lot of questions about the possibility of mutual legal assistance acts by Brazilian authorities. That notwithstanding, there are several arguments which were not presented to those courts that clearly show that the MP has a crucial role to play in international cooperation in criminal matters.