While the majority of the population is now estimated to live in regions with below replacement fertility, high fertility, poor reproductive health outcomes and relatively rapid population growth remain an important concern in several low income countries. International and national spending devoted to family planning, however, has declined significantly in recent years. Recent research has brought about a revision in the understanding of the interactions between population growth and economic development, as well as the effects of family planning programs in terms of reduced fertility, improved reproductive health outcomes and other life-cycle and intergenerational consequences. This paper discusses recent evidence about the benefits of family planning programs and the interactions between population growth and developments, and it attempts to estimate benefit-cost ratios for increased spending on family planning.