This study assesses the state of the art of the measurement and use of estimated economic value, or "shadow prices," in applying benefit-cost analysis (BCA) to social program evaluation. It reviews 39 effective social programs whose effects have been evaluated using scientifically rigorous methods and documents outcomes affected by the programs. The study also reviews the 22 social programs with an associated BCA and the shadow prices used to value benefits. The study finds that many of the important benefits that accrue from social programs are rarely, if ever, monetized; shadow prices for outcomes valued in BCAs do not consistently capture the full range of societal benefits or costs; even where there is a well-established literature for valuing outcomes, the use of shadow prices is not consistent across studies of social programs; and program benefits that extend into the future may be monetized, but uncertainty associated with future costs and benefits needs to be recognized. These findings suggest directions for future methodological work to advance the use of BCA in evaluating the economic returns from social programs. An appendix includes references for individual programs included in the study. (Contains 26 footnotes and 27 tables.)