Clinicians know that breast feeding is crucial to infant health in developing countries, but they may be less aware of the potential longer term health benefits for mothers and babies in developed countries, particularly in relation to obesity, blood pressure, cholesterol, and cancer. The World Health Organization (WHO) recommends exclusive breast feeding (breast milk only, with no water, other fluids, or solids) for six months, with supplemental breast feeding continuing for two years and beyond. Governments in the United Kingdom have adopted this recommendation, but it presents an enormous challenge for countries like the UK and the United States, where breast feeding rates have been low for decades and can seem remarkably resistant to change. In this review, we will focus mainly on developed countries, with reference to the global context. We will summarise the evidence for the beneficial effects of breastfeeding on health, discuss the epidemiology, and provide practical guidance for managing problems associated with breast feeding. We highlight new developments in infant growth charts and current controversies around HIV and donor breast milk.