In adults, distinct microbial communities inhabit different body sites and exert site-specific metabolic functions. However, when and how microbial community structure and function are established in early life have remained elusive. Chu et al. carried out a large population-based cohort study of maternal–infant pairs to determine the composition and metabolic function of the early neonatal microbiota and up to 6 weeks after delivery across several body sites (including stool, oral gingiva, nares, the skin and vagina). The neonatal microbiota was sparsely populated and predominantly comprised taxa of the maternal skin and vaginal microbiota. By 6 weeks, each body niche was enriched for taxa that were characteristic of their adult counterparts, which indicates a common maturation process. In addition, the microbial community function had expanded and diversified. Finally, although patterns of microbial composition in neonates were influenced by mode of delivery at birth, these differences were not present in the infants at 6 weeks of age, which suggests that the maturation of the infant microbiota is mainly driven by body site and not by mode of delivery.