This book investigates the deep economic causes of environmental unsustainability and offers a new vision to rebuild sustainability economics. While sustainability scholars are hard at work with documenting the tangible systemic crisis of our Biosphere, the economic roots of this crisis are rarely exposed, examined nor addressed. This book's central contribution to sustainability studies is to argue that what we should sustain is not economic growth but social-ecological well-being defined as a combination of planetary health, cooperation and justice resulting in human holistic prosperity. The long-term prosperity of humanity indeed relies on generating health and fostering cooperation informed by justice: social-ecological well-being should be the cornerstone of sustainability economics for the 21st century. Within this framework, this book attempts to explain why the three key dimensions of sustainability are jointly in crisis, show what vision can articulate those dimensions to rethink sustainability economics for our century, what practical policies should be undertaken to give life to these visions before concluding on the need to reinvent the narratives that sustain economic analysis. Éloi Laurent is a senior economist at OFCE and teaches at Ponts Paris Tech, Sciences Po, ESSEC business school and Stanford University. He recently published The New Environmental Economics - Sustainability and Justice (Polity Press, 2020), The Well-being Transition: Analysis and Policy (Palgrave, 2021) and the Routledge Handbook of the Political Economy of the Environment (Routledge, 2021).