This contribution focuses on the challenges that regional organizations face as they are increasingly confronted with, and need to respond to, transboundary and global environmental problems. Ever more frequently, environmental issues that begin as matters of national concern rapidly become transboundary in scope. As exemplified by the outbreak of avian flu, integrated national, regional and international efforts are necessary to tackle transboundary environmental issues which, by their very definition, call for a coordinated effort. This article will concentrate on the impact of transboundary environmental challenges on the objectives and functions of the Association of South East Asian Nations (asean).