The aim of this project is to map the healthy gut in infants and children (age 0-5y) during a critical developmental window that impacts long-term health outcomes and is shaped by genetics and the environment. We aim to map early gut development across populations with diverse ancestry and geography, at single-cell resolution, and with linked contextual data on tissue morphology, genetic background, social determinants of health and environmental exposures. The network will involve both rural and urban populations in the US - at sites in Boston, Mississippi and Virginia - and internationally, in Pakistan; it will also include communities that have historically been under-served in ‘omics research.