This paper offers a review of recent literature regarding the take up of social programs in the U.S. and U.K. A few general conclusions are drawn: First, take up is enhanced by automatic or default enrollment and lowered by administrative barriers, although removing individual barriers does not necessarily have much effect, suggesting that one must address the whole bundle. Second, although it may be impossible to devise a definitive test of the ?stigma hypothesis?, other, more concrete types of transactions costs are probably a good deal more important. Third, although people generally have means-tested programs in the United States in mind when they discuss take up, low take up is also a problem in many non means-tested social insurance programs and in other countries. Historically, economists have paid little attention to rules about eligibility, and virtually no attention to how these rules are enforced or made known to eligibles. Hence, the marginal return to new data about these features of programs is likely to be high in terms of understanding take up. In an era of social experiments, it might also prove useful to consider experimental manipulations of factors thought to influence take up.