This chapter evaluates some of the reported infant and maternal benefits of breast-feeding. Breast milk contains several components that promote passive and active immunity. Immunoglobulins (IGs), including IgA antibodies, directed at microbes in the maternal environment, are transferred from the mother to the infant through breast milk. Mothers of breast-fed children may have been more likely to have higher IQs, which may also have been associated with their child's IQ. Higher cognition scores in children who have been breast-fed may largely be attributable to confounding. Lactation may decrease the risk of maternal breast cancer by enhancing the differentiation of epithelial cells in the mammary duct. Lactation may affect the risk of maternal diabetes through improvements in insulin and glucose homeostasis. On the basis of the epidemiological evidence, breastfeeding is a modifiable risk factor for several maternal and child health outcomes.