This chapter examines how “green regionalism,” understood as the incorporation of environmental and climate-related disciplines into trade agreements, affects selected ASEAN member states and creates a persistent compliance gap. Using the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) and the EU–Viet Nam Free Trade Agreement (EVFTA) as two analytically distinct case studies, the chapter does not treat them as ASEAN agreements or as proxies for ASEAN as a whole. Rather, it uses them to illustrate two different pathways through which external green trade disciplines reach Southeast Asia: a plurilateral agreement with an enforceable environment chapter and a bilateral North–South agreement centred on consultation, cooperation, and expert review. The analysis shows that, for the ASEAN parties most directly affected, obligations of non-regression, effective enforcement, and the implementation of multilateral environmental agreements impose demanding requirements for legislative reform, monitoring infrastructure, and administrative capacity. The chapter further argues that ASEAN’s relevance lies not in treaty authorship, but in its potential role as a regional compliance facilitator. Although ASEAN-centered FTAs and RCEP remain relatively light on binding environmental obligations, ASEAN’s soft-law toolkit, policy coordination, and dialogue-partner mechanisms can help diffuse best practices, mobilise technical assistance, and narrow implementation asymmetries. The chapter concludes that green regionalism in Southeast Asia will remain uneven unless high-standard FTAs are matched by differentiated implementation pathways, stronger domestic enforcement, and ASEAN-led mechanisms that support rather than assume compliance.