Programs for the delivery of public goods and services are often more effective if the public participates in their planning and execution. Not all such activities benefit from public participation, however. Activities whose effectiveness most benefits from such participation are those whose local effects are variable; those that have to be made frequently but not routinely; those that require quick responses from the public; and those whose impact calls for major changes in the behavior of the public. Experience with irrigation projects in developing countries is consistent with this “sensitivity hypothesis,” but the hypothesis is probably applicable to the management of other goods and services such as social welfare, education, public health, and transportation.