Social science research has made important contributions to population policy and to the effectiveness of family planning programs. Social science concepts, theories, and methods potentially are relevant to all aspects of reproductive behavior, including actual fertility, proximate variables, and desired family size. Social science research also contributes to the understanding of the social, economic, and political institutions that potentially affect, either directly or indirectly, the whole biosocial reproductive system and family planning programs. At least as important as its specific theories and findings is the role of social science in testing how to adapt such knowledge to distinctive national and local cultural circumstances of family planning programs. A central point is that carefully monitored pilot projects are desirable before launching full-scale national programs, as well as being continuing resources for program development. The research on early programs in Asia has been important, because those programs encountered and overcame some of the presumed obstacles to new programs.