What factors influenced the resurgence of breastfeeding in the last decades of the twentieth century? This article has considered several explanations. Demographic trends, particularly the increased birth rate among black and Hispanic women, coupled with the resurgence of breastfeeding in these groups, may have contributed to the increase in the breastfeeding rate during the 1990s but likely played a minimal role in the earlier, more dramatic increase. The decrease in breastfeeding in the earlier part of the twentieth century may be partly attributable to increased maternal employment, but the resurgence of breastfeeding occurred during the late twentieth century--a period of unprecedented influx of new mothers into the workforce. There is no evidence that health care practitioners are providing more support for breastfeeding, and most international and US policies postdated the resurgence of breastfeeding, although they may have influenced the increase in the 1990s. A more plausible explanation of the resurgence of breastfeeding in all major segments of society is the pervasive influence of the natural-childbirth movement of the 1960s and 1970s, with its effects on the standard management of childbirth. Also, the increase in breastfeeding among low-income women may be attributable partly to programmatic changes in the provision of supplemental food through the WIC program and the targeting of breastfeeding-promotion efforts to the specific concerns of these women. Although breastfeeding increased at the end of the twentieth century relative to earlier decades, the disparity between the recommended rates and those achieved by US women is great. Thus, efforts to increase breastfeeding initiation and duration should continue, particularly for the groups that are at greatest risk for illness, such as minority and low-income infants. This article suggests that the strategies likely to have a lasting effect on future breastfeeding rates will be social pressures that affect existing barriers to breastfeeding. Such pressures may come from health maintenance organizations, insurance companies, and the US government, which are likely to increasingly recognize the costs of not breastfeeding to their institutions. The provision of flexible work hours and paid maternity leave, either by the US government or family-friendly workplaces, could increase the ability of employed women to optimally feed their infants. As Retsinas noted in an article on the cultural context of breastfeeding, "While it is 'known' that breastfeeding is better, our society is not structured to facilitate that choice." Efforts to improve breastfeeding rates need to make visible the wider cultural context in which infant-feeding choices are made and alter components that make it difficult for US women to feed their infants optimally.