There is an intense interest in the effects of breast-feeding on the offspring and in understanding the mechanisms behind these effects. More than 50 papers are published monthly on topics such as the influence of breast-feeding on aspects of growth, immune-related effects, mental development, and noncommunicable diseases. Most breast-feeding data are observational; confounding can be difficult to rule out because some maternal factors are associated with both breastfeeding and infant outcomes (e.g., obesity and mental development). The most important short-term immunological benefit of breast-feeding is the protection against infectious diseases. There is also some evidence of lower prevalence of inflammatory bowel diseases, childhood cancers, and type I diabetes in breast-fed infants, suggesting that breast-feeding influences the development of the infant's own immune system. One of the most consistent findings of breast-feeding is a positive effect on later intelligence tests with a few test points advantage for breast-fed infants. In the last few years, several systematic reviews and meta-analyses have examined the effect of breast-feeding on noncommunicable diseases. There seems to be a small protective effect against later overweight and obesity. Blood pressure and blood cholesterol seem to be slightly lower in breast-fed infants; however, the few studies examining breast-feeding and the risk of coronary heart disease in later life did not find an association. Recent data have suggested that breast-feeding can program the insulin-like growth factor-I axis, as 3 studies found that breast-fed infants are taller as adults. J. Nutr. 137: 503S-510S, 2007.