William Baumol, an economist with several important contributions to our understanding of economics, including environmental economics, has passed away. Professor Baumol published several academic articles in environmental economics and, along with Wallace Oates, he published one of the most influential books in the field: The theory of environmental policy. In the year 2000, professor Baumol published a paper in the prestigious The Quarterly Journal of Economics on the advances in economics in the XX century. In this paper, he includes the development of environmental economics. Professor Baumol was well-known for his cost disease theory about the decline in prices of goods such as cars and household appliances, increase in prices of services such as health and education, and economic growth.