Breast feeding is of central importance to child survival, growth and development, especially in non-industrialized countries. It also protects the mother against further pregnancy. In the light of the increase in the world's population, the implications of the decrease in breast feeding worldwide are serious. There is a direct association between child health and survival and breast feeding. In this paper, the contraceptive effect of breast feeding is reviewed. The emphasis is on families in non-industrialized societies. The importance of suckling frequency and duration, and the timing of introduction of supplementary foods to the baby, are discussed. Limitations of the method, and recommendations to maximize its effectiveness, are given. It is noted that protection of breast feeding both as a means of improving child health and of spacing births will require positive action at local and at governmental levels.