Climate change, mass extinction, deforestation, desertification and increasing pollution and toxicity of the air, water and land: Uncontainable by national borders, these are quintessentially global concerns for which peoples and states have turned to international law for solutions. This edited collection asks how international lawyers have understood the environment: What exactly is it and how do international lawyers purport to govern it? These seemingly straightforward questions have the potential to unmake our discipline through destabilizing formative assumptions about the separation between subjects and objects of governance, between the social and the natural, and between the human and non-human. We explain in this introductory chapter that reexamining international law assumptions about the natural world is not mere theoretical speculation. It is an urgent and necessary step for addressing pressing environmental challenges.