This thesis addresses the implementation of sustainable development in the legal frameworks of regional integration agreements (RIAs). Sustainable development is reaffirmed as one of the main priorities of the international community, while poverty eradication and the integration of socio-environmental concerns into all governance levels remain the most pressing challenges to its implementation. Furthermore, the role of law is considered fundamental for sustainable development, but there remains a lack of analysis of how legal frameworks are effectively advancing this objective. In this regard, the thesis focuses on the laws and policies of two of the most important RIAs in force, the European Union and MERCOSUR, with a twofold objective: 1) to analyze how RIAs can provide enabling legal frameworks for the promotion of sustainable development, going beyond trade liberalization and serving as a building block between multilateral goals and their implementation at the national level; 2) to provide case studies of norms and policies developed at the regional level addressing a) poverty eradication and social justice within their internal spheres; b) trade policies and instruments that more effectively integrate socioenvironmental objectives. The research undertaken has also a comparative element that enables the consideration of whether the EU, a more developed regional organization, can provide lessons to MERCOSUR in advancing these specific issues. The conclusions show that RIAs' legal frameworks can facilitate effective translation of sustainable development goals into concrete norms and policies, bridging the divide between a multilateral system of standard setting with low implementation power, and national states with weakened capacity to deal independently with these issues. The RIAs studied have been developing procedural innovations such as 'impact assessment' instruments, and substantive innovations, such as regional development funds aimed at promoting social cohesion internally, and trade instruments that integrate development concerns in their external relations, such as preferential trade systems (GSP) linked to socio-environmental issues and trade agreements that include 'trade and sustainable development' chapters. It also provides evidence that, despite their institutional differences, the development of sustainable development laws and policies within the EU has followed a path that can provide valuable insights for MERCOSUR. Finally, the thesis argues that, despite the tensions that might arise between the implementation of these regional measures and the multilateral trade system rules, regional action might be a way to cope with the difficulty of reaching a global agreement while also reflecting more adequately local concerns. The challenge is to assure coherence and consistency with the international goals, but given the importance of promoting a more sustainable development process, this a task worth pursuing.