The study deals with the application of mathematical modelling to multiobjective water resources planning. Such planning is seen as the selection and quantification of the various planning objectives, the formulation of technologically feasible plans which are efficient in the Pareto sense and finally screening of plans for political feasibility. Aspects of political decision-making which are relevant to multiobjective planning are reviewed, as are current Federal guidelines for multi to multiobjective planning and techniques for quantifying water-resource planning objectives. A general framework for the application of mathematical models to multiobjective planning is developed. Optimization and simulation models are seen as useful in two planning stages. Examples and case studies of both types of applications are presented. (Modified author abstract)