Gut health, manifested by the state of the gut microbiome, is established during development, pre-, peri-,and postnatally. The developmental exposome which includes various maternal microbiomes, birth mode, breastfeeding, early infections, and antibiotic treatment, importantly influences the fetal gut microbiome maturation. While the microbiome is malleable throughout life, microbiome susceptibility to environmental influences is highest in early life. This makes the microbiome a potential key player in the Developmental Origins of Health and Disease which connects early life stressors with subsequent chronic disease incidence. Infant gut health may mediate the influence of the early environment on both short-term and long-term disease risk.