Robert Underwood Ayres (born June 29, 1932) is an American-born physicist and economist. His career has focused on the application of physical ideas, especially the laws of thermodynamics, to economics; a long-standing pioneering interest in material flows and transformations (industrial ecology or industrial metabolism)—a concept which he originated. His most recent work challenges the widely held economic theory of growth.
Trained as a physicist at the University of Chicago, University of Maryland, and King's College London (PhD in Mathematical Physics), Ayres has dedicated his professional life to advancing the environment, technology and resource end of the sustainability agenda. His major research interests include technological change, environmental economics, "industrial metabolism" and "eco-restructuring". He has worked at the Hudson Institute (1962–67), Resources for the Future Inc (1968) and International Research and Technology Corp (1969–76). From 1979 until 1992 he was Professor of Engineering and Public Policy at Carnegie Mellon University, Pittsburgh, Pennsylvania, except for two years (and six summers) on leave at the International Institute for Applied Systems Analysis (IIASA) in Laxenburg Austria. In 1992 he moved to the international business school INSEAD in Fontainebleau, France as Sandoz (later Novartis) Professor of Environment and Management. Since his formal retirement in 2000 he has been Jubilee Visiting Professor (2000–2001) and king Karl Gustav XVI professor of environmental science (2004–2005) at Chalmers Institute of Technology Gothenburg (Sweden). He is currently an Institute Scholar at IIASA.