Aggregate measures of contraception, marriage, induced abortion, and lactational infecundability were proposed and successfully used to account for variations in aggregate fertility. The potential supply of surviving children in the absence of fertility regulation is largely determined by factors explaining natural fertility. The dependent variable in the controlled fertility equation is the number of children born after initial use of contraception. The coefficient for duration of use can be interpreted as the number of births averted with one year of contraception. Contraception in rural Egypt does have a clear and strong impact on fertility, leading to low fertility levels while it is used. Such impact is probably comparable to the effects of contraception elsewhere—in both developing and developed nations. This finding does not imply that efficacy cannot be improved, but suggests that much larger fertility declines may be realized by fostering contraceptive adoption and continuation than by attempting to heighten contraceptive efficacy.