A feature of the evolution of lactation is the explicit development of a symbiotic relationship between microbes and the mammalian host. This relationship is emerging as a key process of proper development. Human milk feeds and guides the colonization of the infant gut microbiota and nourishes the phenotypic state and metabolic processes of bacteria evolved to this unusual ecological niche. A milk-oriented microbiota (MOM) sets the infant up for a lifetime of health. The crosstalk between maternal milk and the infant gut has been the focus of research of an interdisciplinary and highly integrated team, the Milk Group, at UC Davis, for the past decade. Megan's group have used the insights gained from basic science research to steer the development of clinical solutions. Interestingly, one of the most abundant components of human milk, oligosaccharides, provides no direct nutritional support to the infant. Instead, they have shown that these complex sugars actually selectively promote the growth of beneficial bacteria in the gut while excluding potential pathogens. The specificity of this interaction is a key principle to understanding how the microbial ecology of the intestine goes wrong promoting conditions like irritable bowel syndrome in adults and necrotizing enterocolitis in preterm infants. This paradigm has been utilized in recent clinical trials with success, and we have also began to examine the gut microbiota-brain axis in neurodevelopmental disorders such as autism.