Exposure to microbes in utero impacts fetal development. Appropriate colonization is associated with healthy immune defense mechanisms whereas inappropriate colonization can result in immune-related disease in later life. An important environmental factor influencing the nature of colonization is diet. Oligosaccharides contained in human breast milk have been found to effect intestinal microbiota. In this Nestlé Workshop, the importance of microbiota in the setting of both health and disease has been addressed.