International environmental law (‘IEL’) began to emerge as a distinct subdiscipline of international law in the 1970s. Since then, it has assumed critical importance in helping to maintain the ecological systems upon which all life on planet Earth depends. It is continuing to develop and is relevant to all states and communities, affecting a wide range of human activities and concerns. This chapter briefly traces the history of IEL and sets out some recent institutional and policy developments, including the United Nations Environment Assembly and the UN Sustainable Development Goals. It also looks at concerted attempts to fill gaps in the field. Given the vastness of the subject matter, the chapter does not purport to be a comprehensive or in-depth analysis. It addresses the main organising principles of IEL, both established and emerging. It provides an overview of treaties (also referred to as multilateral environmental agreements or ‘MEAs’) in several key subfields, including regimes addressing the atmosphere, transboundary pollution, chemicals and wastes, biodiversity, and land degradation. It also includes a case study on world heritage and its implementation in Australia.

This chapter examines the ICJ’s influence on international environmental law. Drawing on concrete examples, the author identifies six ways in which the Court’s jurisprudence has contributed to environmental law: by articulating foundational principles; by acting as a gatekeeper for customary international law; by elaborating existing principles; by interpreting environmental agreements; by valuing environmental harms; and by incorporating environmental considerations into other areas of international law. The author reflects on potential future evolutions of the Court’s role in the international environmental law space, given the increasing number of disputes that the Court has addressed in this field in recent years.