Sustainability has emerged as a major theme in planning. Urban environmental planners frequently recommend greenways as one approach to making places greener, healthier, and more livable. This case study examines whether the greenways system in Indianapolis, Indiana, is sustainable using a framework based on six principles of sustainability recently proposed in the planning literature. Goals of the green-ways master plan are linked to principles of sustainability, and indicators from an ad hoc set of empirical studies of the greenways are used to assess progress towards goals and sustain-ability. Planners can apply this framework elsewhere by linking goals developed in local planning processes to these principles, using available information to develop indicators, and, as part of continuing, iterative planning processes, designing data collection programs that yield more comprehensive sets of indicators over time.