The Microbiome in Prenatal and Neonatal Life clarifies that the microbiome in the maternal fetal unit and immediate changes that occur as new microbes are acquired postnatally play major roles in subsequent health and disease. Rapidly developing technologies for multi-omic analyses and systems biology are shifting paradigms in both scientific knowledge and clinical care with regard to this topic. In essence, we are changing the idea that newborns emerge from sterile environments. As such, in-utero colonization may have impacts on the development of immunity and metabolism that, with epigenetic modifications, will lead to diseases in later life. In addition, the microbial profile that develops during and after birth depends on mode of delivery, type of feeding (human milk versus formula), and various other environmental factors to which the newborn is exposed.