During the last ten years or so since 1992 Rio Earth Summit,there has been a virtual explosion of regional activity for environmental protection in Northeast Asia (NEA). Environmental cooperation has been institutionalized at both bilateral and multilateral levels and various projects to curb regional environmental problems have been adopted and implemented. The environment became reformulated as a regional political issue. Environmental cooperation in NEA shows an interesting characteristic in progress. Countries have developed formal cooperation at bilateral level by concluding either environmental treaties or agreements and setting up joint committees for implementing cooperation. Although less formal then bilateral cooperation, cooperation at the multilateral level also has shown a steady progress. Norms for collective action were firmly established and institutional arrangements were agreed. However, overall, environmental cooperation in NEA has been progressing into non-binding cooperation without clauses clearly describing official commitments for compliance and legal restrictions for non-compliance at either bilateral or multilateral cooperation. Adopting conventions or protocols has been avoided or rejected in negotiations. Why environmental cooperation in NEA is non-binding? This paper is an attempt to answer the question by exploring the progress of environmental negotiation in the region. Considering that environmental cooperation is a foreign policy issue of countries, the non-binding cooperation in NEA are policy choices of countries. By exploring political, economic, and environmental interests behind positions of countries in environmental negotiation, the paper concludes that the non-binding commitment for environmental cooperation could be a rational policy choice of countries in the region. In exploring countries’ interests in environmental politics in NEA, archival research, document analysis, and particularly, extensive elite interviews were applied to collect qualitative data. Elite interviewing was in particular an excellent form of data collection for this paper since the behavior of interests can be best described and explained by those who are deeply involved in policy-making processes. In this research, the validity of interviewees’ statements was determined by examining their plausibility, checking for internal consistency, referring to documents and reports from the government, research institutes, and environmental NGOs, and corroborating with other interviewees. [ABSTRACT FROM AUTHOR]