My talk will cover how the microbiome develops in term infants and preterm infants. Within preterm infants, I will discuss how diet-microbe-host interaction has been linked to a range of health and disease outcomes, including necrotising enterocolitis. I will introduce a preterm human intestinal organoid model system we are using to advance our gut microbiome work. Such work has potential to develop novel disease biomarkers and targeted therapeutic interventions to promote health in preterm infants.