The sustainability of development presents some of the most important policy challenges concerning the future of our planet. None of these central issues can be understood from the sole perspective of a traditional discipline, whether in the social, natural, engineering, or health sciences. The PhD in Sustainable Development combines a traditional graduate education in the social sciences, particularly economics, with study in the natural sciences and engineering, to prepare scholars who are uniquely situated to undertake serious research and policy assessments in furthering the goal of sustainable development. The program includes a set of rigorous core requirements in the social and natural sciences designed to provide a deep understanding of the interaction between natural and social systems, and provides students with the flexibility to pursue in-depth research in a broad variety of critical policy areas, ensuring that they cultivate both a unique combination of diverse skills and deep insight into the most challenging problems of future human welfare. Together with experts and faculty at Columbia, students in the program conduct research in a wide variety of areas including climate change and its social consequences, causes and solutions to extreme poverty, energy systems, agricultural transitions, water resources, infectious disease, global demographic change, ecosystems, disasters, and conflict. Students also benefit from being part of the Earth Institute's research and practice programs that focus on sustainable development.