The three main objectives of the study are to conduct a comprehensive analysis of the legal and institutional foundations of regionalization, identify the key characteristics and features of this phenomenon, and assess its impact on national legal systems and international relations. Although there are numerous publications devoted to local cooperation mechanisms around the world, most of them focus on political and/or economic integration and ignore the legal aspects of regional integration. The manuscript examines the key theoretical approaches, institutional mechanisms, and legal frameworks that ensure sustainable development of regional associations. It delves into the phenomenon of legal regionalization, highlighting various challenges that arise in specific regional contexts. The results of the study illustrate that the success of regionalism requires strong institutional structures, harmonization of legal norms, and consideration of socio-cultural factors. Eurasian cooperation is at the stage of regionalization, but has not yet developed into full-fledged regionalism, which is more formalized. The article contributes to understanding the dynamics and complexities of the new wave of regionalization, providing scholars, policymakers, and practitioners involved in international cooperation and integration with insights based on the analysis of integration processes. The manuscript enriches the academic discussion of regionalization by providing insights into its possible implications for international relations and international law.