The global future lies before us as a highly uncertain and contested landscape with numerous perils along the way. This study explores possible pathways to sustainability by considering in quantitative detail four contrasting scenarios for the twenty-first century. The analysis reveals vividly the risks of conventional development approaches and the real danger of socio-ecological descent. Nonetheless, the paper underscores that a Great Transition scenario—turning toward a civilization of enhanced human well-being and environmental resilience—remains an option, and identifies a suite of strategic and value changes for getting there. A fundamental shift in the development paradigm is found to be an urgent necessity for assuring a sustainable future and, as well, a hopeful opportunity for creating a world of enriched lives, human amity, and a healthy ecosphere.