William Clark is the Harvey Brooks Professor of International Science, Public Policy and Human Development at Harvard University's Kennedy School of Government.

Trained as an ecologist, his research focuses on the interactions of environment, development and security concerns in international affairs. He has studies underway on the design of research systems for sustainability science, development of better assessment frameworks for use in the management of global environmental change and on the problems of monitoring and evaluating progress towards sustainable development. Clark is an active member of the Sustainability Science Initiative, chairs the Design Committee for the Heinz Center's report on the State of the Nation's Ecosystems, and recently co-chaired the sustainability transition study of the US National Research Council. He serves on boards and advisory committees for the International Human Dimensions Programme on Global Environmental Change, the Potsdam Institute for Climate Impacts Research, and the Heinz Center for Science, Economics and the Environment. At Harvard, Clark has served as Vice Chairman of the University Committee on Environment, member of the Steering Committee of the Center for International Affairs, and Director of the Center for Science and International Affairs.

He is co-author of Redesigning Rural Development (Hopkins, 1982) and Adaptive Environmental Assessment and Management (Wiley, 1978); editor of the Carbon Dioxide Review (Oxford, 1982); and coeditor of The Earth Transformed by Human Action (Cambridge, 1990), Sustainable Development of the Biosphere (Cambridge, 1986), Learning to Manage Global Environmental Risks (MIT, 2001), and Environment magazine. Clark was awarded the MacArthur Prize in 1983.