This Element examines the legal infrastructure required to address the intertwined health and environmental crises of the Anthropocene. It introduces planetary health law as an emerging transdisciplinary paradigm that integrates global health law and international environmental law to tackle the impacts of climate change, biodiversity loss, and pollution on humanity and the broader biosphere. The Element highlights the shortcomings of current frameworks, which remain largely voluntary and anthropocentric. It makes the case for a comprehensive planetary health law framework that recognizes both the human right to a healthy planet and the planetary right to health. This integrated approach would catalyze systemic institutional reform. Key proposals include the creation of a Planetary Health Organization to coordinate the work of the World Health Organization and the United Nations Environment Programme, alongside a Planetary Health Tribunal to enforce Nature-oriented norms and accountability. This title is also available as Open Access on Cambridge Core.