Engrossing, thought-provoking, and troubling, Patrick McCully’s well-documented and carefully researched study of large and major dams concludes that their era, much like that of fossil fuels, is drawing to a close. Two main theses dominate this study. First, large dams as a group have not provided an adequate economic Book Reviews 285 or social return on their substantial investments (two trillion dollars), especially in developing countries, where the money could be better invested elsewhere. Second, long-term, independent, postconstruction, comprehensive benefit/ cost studies of large dams are rare to nonexistent. Instead, the industry-wide trend is to overstate benefits and understate or even ignore costs, and to terminate all investigation shortly after the last bucket of concrete is poured. Time and again, even the most basic hydrologic data—a critical input for efficient dam design and operation—are badly flawed, due to either an actual absence of reliable long-term data or unjustifiably optimistic projections.