Breastfeeding is one of the best public health “buys” available for countries at all levels of development. In the first year of life, appropriate infant nutrition (exclusive breastfeeding to around 6 months) reduces infant mortality and hospital admissions by 50% or more. Early life nutrition has important influences, including on childhood illnesses, obesity, cognitive development, hospitalizations, and later chronic disease. Breastfeeding is consistent with the historical cultural practices of all societies, and its benefits of breastfeeding last a lifetime. While the development of infant formula has been of benefit to some infants, its inappropriate promotion has resulted in a decline of breastfeeding, and, as a result, health gains in many countries have not been as great as they could have been. The health benefits of breastfeeding will provide some protection against the effects of climate change, which will cause a decline in potable water supplies and increases in the incidence of some infections. Infant formula production has very high environmental costs, while breastfeeding as well as being the best infant feeding intervention also has very low environmental impact. An important part of the sustainable development agenda must be to promote breastfeeding and its benefits and to reverse the inappropriate promotion and use of infant formula.