Every September and October, entities in the palm oil and timber industries in Indonesia conduct slash-and-burn activities over peat land, causing transboundary ‘haze’ pollution. This paper analyzes the effectiveness of various legal solutions to tackle the transboundary haze pollution. There are mainly three forms of international law, customary international law, the ASEAN Agreement on Transboundary Haze 2002 and Singapore’s extraterritorial Transboundary Haze Pollution Act 2014. Their effectiveness will be measured by Indonesia’s increasing willingness to take domestic enforcement measures. This paper argues that the ASEAN Agreement is the primary instrument despite its lack of sanctions as it is neutral, non-confrontational and consistent with the ‘ASEAN way.’ The Singapore Act plays a complementary role, yet its invocation may strain relations between Singapore and Indonesia. Ultimately, the three forms of international law serve as a normative and facilitative source in nudging Indonesia to take more stringent domestic enforcement measures.

I. Introduction
 II. The Sources of International Law againstthe Haze of Indonesia
  A. Customary International Law
  B. Multilateral Instruments
  C. Singapore’s Extraterritorial Legislation
 III. What Has Been Done by Indonesia?
 IV. Measuring Effectiveness of the ASEANAgreement and the Singapore Act
  A. Measuring Effectiveness of International Environmental Agreements
  B. Measuring Effectiveness of the ASEAN Agreement
  C. Measuring Effectiveness of the Singapore Act
  D. Analysing the Role of Third Parties
 V. Conclusion

• Kexian Ng(LL.M. Representative and Executive Board Member of Columbia Society for International Law.)