Social experiments provide the most reliable guide to potential impacts of policy change because their methodology allows analysts to isolate the effect of the policy change from other, potentially distorting factors. This revised and updated edition of the Digest of Social Experiments documents 241 completed and 21 ongoing social experiments. In addition to the findings, each summary details target populations, policies tested, experimental designs and related issues, sites, key staff, sources of further information, and public access to the data. The authors also discuss the theory and practice of social experimentation, the reasons for conducting social experiments, the ethical issues, and non-experimental methodologies that have been proposed as substitutes. They examine the uses of social experiments in the policy process, and offer a brief history of social experimentation.