In the developing countries in recent years there has been a great expansion of public programs to provide modern means of fertility control. This paper is an effort to appraise the demographic impact of such programs through a comprehensive evaluation of the record. The paper briefly reviews the criticisms of such programs and the historical and comparative background before turning directly to issues of performance. After establishing the broad range of acceptance, the paper reviews the nature of acceptors and of fertility control methods as they affect overall impact. Then follow a series of tabulations and analyses of country performance by both social setting and program effort in an attempt to discern the effect of "modernization" and "family planning" in line with the current controversy over their relative importance. That detailed analysis is followed by an extensive review of 14 country cases, similarly organized, plus brief summaries of 15 major experiments/demonstrations in this field and one example of a developed country program. After a brief section on the alternatives to family planning programs, the paper concludes with a summary of major findings-underlined in the text-and the authors' personal commentary on their implications for both study and action.