This text develops a decision support methodology for strategic environmental decision problems and provides several generic as well as specific tools. The proposed methodology is based on modelling the underlying physical and economic processing. These substantial models are used for single criterion optimization and for multi-objective model analysis based on the reference point approach. It is shown that in this way, learning and decision processes may be supported, using concepts like soft constraints, inverse simulation and search for compromise solution. The last section consists of four chapters on applications. Each chapter treats an area of environmental decision making: water quality management in river basins, land use planning, cost-effective policies for improving air quality, and energy planning. For each area decision support systems are presented and it is shown how they are used for supporting decision making and negotiations.The applications as well as the methodology presented in this book have been developed at the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria, in close co-operation with several other institutes and organizations. It should be of use to researchers and practitioners in the fields of environmental modelling and analysis, decision support, mathematical programming and political analysis.