As scientists depict six planetary boundaries as transgressed, they have called on international lawyers to develop “legal rules of the game” to safeguard the Earth's ecological limits. How can the law help protect the Earth's life-support systems at a time when humanity is pushing the planet beyond its safe limits? In recent years, courts have increasingly acknowledged the existence of planetary legal limits, especially in tackling climate change and biodiversity loss. While incremental processes of legal evolution continue at various levels it may well be that they do not unfold fast enough to reign in planetary crises given current geopolitical and geoeconomic realities. Recognizing the urgency of these crises, Governing Planetary Ecological Boundaries merges classical rule of law theory with insights from Earth system science to develop the concept of a planetary rule of law that integrates a “safe and just” operating space with core rule of law requirements.The book assesses international climate law, international biodiversity law, the law of the sea, human rights law, and constitutional law to reveal achievements in operationalizing existing limits for individual governments, but also severe issues in adjudication and enforcement. Accordingly, it advocates for several innovative reform proposals de lege ferenda ranging from planetary constitutionalism and the global expansion of unilateral regulation to reduce the planetary footprint of economies, to the development of plurilateral climate or planetary clublike structures. It also emphasizes the need to strengthen, in legal terms, the adaptive capacity and resilience of humanity, particularly its most vulnerable population