One of the major goals of family planning programs worldwide has been to reduce the level of fertility in hopes of slowing the rate of natural increase and promoting social and economic development. Such programs have now been in existence for sufficient lengths of time to have had an impact on fertility levels. In several countries with organized family planning programs, marked declines in fertility levels have been observed. The extent to which such declines may be credited to organized programs has not been rigorously measured because an appropriate research methodology has been lacking. This paper describes one method of directly linking declines in fertility levels to the contraceptive protection experienced by a population. The contribution of organized family planning programs is estimated by decomposing the amount of total contraceptive protection into within-program and outside-program sources.