William E. Rees

William E. (Bill) Rees, PhD, FRSC, is a Canadian human ecologist, ecological economist and Professor Emeritus at the University of British Columbia in Vancouver, Canada, where he taught and conducted interdisciplinary research for more than four decades. He is perhaps best known for co-developing the ecological footprint concept and method of analysis with his graduate students.

This quantitative tool estimates humanity's demand on nature, through measurable flows of energy and materials to and from ecosystems; it thus reinforces associated concepts such as ecological limits and biocapacity, and shows clearly that the human enterprise is in a state of advanced ecological overshoot.

Rees' work has long focused on the relationship between the human enterprise and the ecosphere, sustainability, human carrying capacity, over-exploitation, ecological overshoot, and urban systems and on cognitive barriers to understanding the depth of our eco-predicament. He has authored or co-authored hundreds of peer-reviewed papers and popular articles on these issues. His work is taken up by governments, nongovernmental organizations, educators, and scholars internationally.