The Problem Economic efficiency is naturally thought to be a virtue of social policies and decisions, and cost-benefit analysis is commonly regarded as a technique for measuring economic efficiency. It is not surprising, then, that CB analysis is so widely used in social policy analysis. However, there is a great deal of controversy about CB analysis, including controversy about its underlying philosophical rationale. The rationales that have been proposed fall into three basic, though not mutually exclusive categories. There are moralist (...) views to the effect that an acceptable CB analysis would provide, or contribute to, an ethical appraisal of proposed policies or projects. There are rationalist views to the effect that an acceptable CB analysis would contribute to the selection of social policies and projects that are “socially rational.” Finally, there are so-called management science views to the effect that the purpose of CB analysis is to promote the achievement of objectives held by the policy maker, whatever they may be. Different positions are available within each of these categories. But there is also the possibility that CB analysis lacks any viable rationale. I will examine some of the major rationales for CB analysis in this paper, and I will suggest that the last view is close to the truth. (shrink)