This paper, which provides background for other papers in the volume, first reviews the nature and development of water resources planning and evaluation criteria at the Federal level in the United States. These criteria constitute a highly developed, complex set of guidelines for project planning and evaluation. The level of development of these criteria and their long historical development from theoretical foundations must be taken into account in relating global climate change to possible changes in planning criteria. Second, the essentials of water project planning and evaluation, including benefit-cost principles and more complex concepts of social decision-making, are outlined. Third, the paper provides an overview of global climate change assessment methods, including impact assessment and integrated assessment. Impact assessment uses a relatively straightforward comparison of with and without situations; integrated assessment attempts to improve on impact assessment by developing more complex models that incorporate a range of feedbacks and interrelationships.