The Islamic Republic of Iran pursued a frankly pronatalist policy during the first decade of her life. The result was a tremendous rise in fertility and the population rose at an annual rate of 3.9 percent between 1976-1986. Partly in response to this rapid growth, the government adopted an anti-natalist policy and the long suspended national family planning program was revived in 1989. The program has proven exceptionally successful both in terms of contraceptive prevalence rate and a sharp decline in fertility. The aim of this paper is to describe the development, organization, and achievements of Iranian family planning program and to identify some of the main factors that may have contributed to its remarkable success. To this end, the main findings of all censuses and surveys conducted by the Statistical Centre of Iran (SCI) and the Ministry of Health and Medical Education (MOHME) between 1976-2000 are reviewed. The findings indicate a tremendous rise in contraceptive prevalence rate as well as a striking decline in fertility and population growth rates since late 1980s. Over 70% of eligible are found to be using a contraceptive. The traditional urban-rural gap has narrowed considerably. Although the large majority of couples are using modern methods, including male and female sterilization, a large proportion continue to rely on coitus interruptus. The use of the latter method is surprisingly more common in urban areas of the better-developed provinces with remarkable rates of fertility decline. By late 2000, 23 of the 29 provinces had CPRs above 70%. Even the two provinces with the lowest CPR level (Sistan-Baluchistan and Hormozgan provinces bordering Pakistan and the Persian Gulf) have higher contraceptive use rates (41.5 & 55%) than most neighboring countries. The fertility rate, which had declined from a TFR of to a TFR of 2.6 between 1986-1996, has continued to fall further. According to large-scale 2 surveys conducted by the SCI (1998-9) and MOHME (2000) the TFR has dropped to below 2 in urban areas of the majority of provinces as well as the rural areas of several provinces. Government commitment, whole hearted support of the politically dominant religious leadership, and the integration of reproductive health services with the extensive primary health care network of Iran are identified as the main factors underlying the unexpected success of the revived family planning program in Iran. Official government promotion of birth control and the support of the politically dominant religious leaders has not only helped to legitimize contraceptive use but it has also eliminated most of the physical barriers to family planning, particularly among the rural and lower class urban couples. The present analysis also calls attention to the importance of such socio-economic factors as urbanization, modernization, expansion of educational opportunities, particularly for women, raised expectations regarding the future education and employment of children, improved general health and lower infant mortality rates, and access to modern means of communication and comfort. The importance of these factors is underlined by the fact that there were signs of rising contraceptive use and fertility decline even before the change in government policy in 1989. It is also noted that a striking rise in age at first marriage has taken place despite continuing government efforts to promote and reinforce early marriage as a religious value. Nevertheless, marriage remains more or less universal and there is strong evidence that the bulk of the observed decline in fertility is due to contraceptive use by married women.