This report investigates the international law and policy challenges to the determination of the international shipping industry's contribution to climate change mitigation efforts through the International Maritime Organization (IMO), a specialized agency of the United Nations and the competent intergovernmental organization with respect to shipping in international law. The report sets out the international legal framework that serves as context for the IMO efforts, the challenge of regulating greenhouse gas emissions from international shipping and the process and issues in determining the industry's 'fair share' of mitigation efforts and potential legal pathways. The report concludes with general, policy and legal considerations that have a bearing on the current and possible future directions of the nascent IMO strategy and potential legal pathways.