Per-Olov Johansson is Emeritus Professor in the Department of Economics at Stockholm School of Economics. He has published four books with Cambridge University Press: The Economic Theory and Measurement of Environmental Benefits (1987), Introduction to Modern Welfare Economics (1991), Cost-Benefit Analysis of Environmental Change (1993), and Evaluating Health Risks: An Economic Approach (1995). Bengt Kriström is Professor of Resource Economics and Head of the Department of Forest Economics at the Swedish University of Agricultural Sciences, Umeå. He has been a consultant to the Swedish Government and to the OECD on many occasions, and has been a member of the Prime Minister's Commission on Sustainability and Chair of the Expert Group on Environmental Studies at the Ministry of Finance.