Breast milk is the best nutrition for new-borns and it supports an optimal growth and development of infants. It even has effects beyond nutrition as it has a complex composition, providing specific bioactive components. During this presentation, Professor Maria Carmen Collado explains that these bioactive components play a crucial role in the development of the gut microbiota and immune system. Perinatal factors shape breast milk composition and infant gut microbiota development. Specific milk microbes, oligosaccharides and microbial metabolites are key in driving infant gut colonization. Alterations in the adequate infant gut microbial colonization are associated with a higher risk of developing non-communicable diseases later in life such as obesity, allergies, diabetes and immune-related problems.