Most of the population of less developed countries (LDCs) now lives in countries with national family planning programs to reduce fertility and improve family welfare. Such programs are a new phenomenon. In some LDCs increasing birth-control practice and fertility declines occurred along with considerable social and economic development, but even there rapid changes among the disadvantaged masses are generally associated with strong family planning programs. Fertility has also fallen in some countries with only some development but with vigorous family planning programs. China, Indonesia, Sri Lanka, and Thailand are such cases. In such places as sub-Saharan Africa and South Asia, fertility generally remains quite high, apparently because of little development and traditional familial institutions. Even in these situations, however, there are examples of significant fertility declines, in some cases nationally and in other cases in intensive, high-quality pilot projects that have established the latent demand for family planning.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66637/2/10.1177_000271629051000103.pd