Confounding all conventional wisdom, the fertility rate in the Islamic Republic of Iran fell from around 7.0 births per woman in the early 1980s to 2.1 births per woman in 2000. That this, the largest and fastest fall in fertility ever recorded, should have occurred in one of the world's few Islamic Republics demands explanation. The paper addresses this issue in three parts. The second part is its core: a description of fertility levels, trends and patterns in Iran by rural and urban areas and provinces in the 1972-2000 period. Own-children data from the 1986 and 1996 Censuses as well as the 2000 Iran Demographic and Health Survey (IDHS) allow us to analyse single-year movements of fertility over the last three decades. This demographic description is proceeded by a socio-political history of Iran in the years 1970-2000, providing a context for the demographic changes. We conclude with some speculations linking specific socio-economic and political changes to the demographic change. Our concluding arguments suggest continued low fertility in Iran.