Water resources professionals have an obligation to conceive and manage water resource systems so that they will fully contribute to an improved quality of life. Those sustainable water resource systems will be able to satisfy the changing demands that will inevitably be placed on them, without significant system degradation. An international group of experts has reviewed various guidelines for achieving greater degrees of sustainability and the extent to which they have been applied in a number of case studies. The group provides approaches for measuring and modeling sustainability and ways in which these measures and models might be used when evaluating alternative designs and operating policies are illustrated.