Relations between the Association of Southeast Asian Nations (ASEAN) and the European Union (EU) have enriched the multifaceted concept of interregionalism from legal and international relations perspectives. The article argues that the transformative ASEAN-EU frameworks have shaped the Third Interregionalism. Brussels’ building-block approach envisions pathfinder agreements with individual ASEAN states as the basis for the ASEAN-EU FTA, which will help realize the EU’s Indo-Pacific strategy and the ASEAN-EU Strategic Partnership. The designs of the EU’s trade and investment agreements with Singapore and Vietnam are therefore critical. The article assesses core areas such as tariff liberalization and ASEAN cumulative rules of origin, as well as commitments of trade in services and non-tariff barriers in key industries. Contributors to the special issue further analyse cutting-edge issues involving electronic commerce and sustainable development. These on-the-ground insights contribute to a new understanding of ASEAN-EU legal frameworks and evolving interregionalism in the post-pandemic era.