Sergio Rinaldi is Professor of Systems Theory at the Politecnico di Milano, Italy, since 1978. He graduated in Engineering at the same school in 1964, and has been working, since then, on dynamical systems and optimal control with particular attention to applications in natural resources management and population dynamics. He is the author of more than hundred papers published in international journals and of three books among which Modelling and Control of River Quality (McGraw Hill, 1979). Sergio Rinaldi has been Visiting Professor at Stanford University, UC Berkeley, UBC Vancouver and Kyoto University and Research Scholar at IIASA, Laxenburg, Austria. He is Associate Editor of Ecological Modelling, Applied Mathematics and Computation, Advances in Engineering Software, and Stochastic Hydrology and Hydraulics and Director of the Research Center for Environmental Modelling (CIRITA), Politecnico di Milano. In 1988 Sergio Rinaldi was awarded the Italgas Price for Scientific Research and Innovation.