The persistence of high rates of fertility in Bangladesh, despite the poverty of its population, has been given alternative, and apparently competing, explanations, including the absence of effective forms of family planning, the resilience of pro-natalist values and norms and the existence of material constraints which led to the reliance on children as economic assets. The recent and dramatic declines in fertility rates, in the absence of any apparent major economic changes in the decades prior to the onset of fertility decline, appears to contradict materialist explanations for fertility behaviour and to support explanations which stressed ideas about the acceptability of birth control and the availability of the means for doing so. This article argues that such an interpretation is based on an historical analysis of events in Bangladesh. It offers an alternative explanation which stresses socio-economic change as the primary motor for change in family size preferences, but which recognises the role of modern forms of family planning in facilitating the pace of the resulting fertility decline.