Mother's milk provides a wide variety of health benefits for infants, which is why breast feeding is highly recommended all over the world. This monograph provides details about the nutritional and bioactive properties of human milk, explaining the significance of this natural source of food. Chapter One describes how lactic acid bacteria present in human milk plays a critical role in establishing an immunocompetent microbiome in new-borns, inducing multifarious health-promoting activities required to successfully initiate the life process. Chapter Two describes how the fatty acid profile of breastmilk varies according to the needs of the infant, particularly depending on the gestational age of the new-born, but also as a result of the mother's diet. Chapter Three summarises the current literature on the composition of human milk and its life-course functional effects on health outcomes.