Dr. Sven Erik Jorgensen is a professor of environmental chemistry at Copenhagen University. He received a doctorate of engineering in environmental technology and a doctorate of science in ecological modeling. He is an honorable doctor of science at Coimbra University, Portugal, and at Dar es Salaam University, Tanzania. He was editor in chief of Ecological Modelling from the journal's inception in 1975 to 2009. He has also been the editor in chief of Encyclopedia of Ecology. In 2004 Dr. Jorgensen was awarded the Stockholm Water Prize and the Prigogine Prize. He was awarded the Einstein Professorship by the Chinese Academy of Science in 2005. In 2007 he received the Pascal medal and was elected a member of the European Academy of Science. He has written close to 350 papers, most of which have been published in international peer reviewed journals. He has edited or written 64 books. Dr. Jorgensen has given lectures and courses in ecological modeling, ecosystem theory, and ecological engineering worldwide. Dr. Fu-Liu Xu is a professor at the College of Urban and Environmental Sciences, Peking University, China. He received his Ph.D. from the Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Denmark. His research interests include ecosystem health and ecological indicators, system ecology and ecological modeling, ecotoxicology and risk assessment of POPs. Dr. Robert Costanza is the Gordon and Lulie Gund Professor of Ecological Economics and founding director of the Gund Institute for Ecological Economics at the University of Vermont. His transdisciplinary research integrates the study of humans and the rest of nature to address research, policy and management issues on multiple scales, from small watersheds to the global system. He is co-founder and past president of the International Society for Ecological Economics, and was founding chief editor of the society's journal, Ecological Economics. He has published over 400 papers and 20 books. His awards include a Kellogg National Fellowship, the Society for Conservation Biology Distinguished Achievement Award, and a Pew Scholarship in Conservation and the Environment.