Over the past three decades, with a combination of new technology, rising female literacy rates, and strengthened family planning programs, the world has seen dramatic increases in the use of contraception, with corresponding declines in fertility and population growth rates. At the International Conference on Population and Development, Cairo in 1994, parties pledged a tripling of funding for reproductive health programs in developing countries. Many demographers believe that making such programs more widely available to women would extend the decline in birth rates and shift the world towards the low scenario of United Nations population projections over the next century and a half. By examining the costs and impacts of such programs, in view of the links between population and carbon emissions, this paper shows that extension of voluntary family planning could make a large and cost-effective contribution to the greenhouse gas limitation goals of the Kyoto Protocol that was negotiated in 1997.