Humans maintain a diverse, dynamic, and complex intestinal microbiota that performs a multitude of vital functions, such as growth and development of the epithelial barrier, stimulation of intestinal angiogenesis, regulation of nutrition, metabolic functions, and education of naïve neonatal innate immunity. After birth, host environment and attributes lend and opt for a stable intestinal microbiota for long-term symbiosis. Dysregulation (dysbiosis) of this process during the early postnatal period can form the basis for later inflammatory, immune, and allergic disorders. The initial immunologic exposure of neonates has long-term consequences. Because of this remarkable influence of microbiota on health and disease, learning about characteristics of microbiota and the factors that modulate it has become the focus of ongoing research. Further knowledge in this field should assist in developing strategies to promote health and prevent diseases. This article reviews recent advances in the understanding of microbiota.