There are over 200 different structures of HMOs in human breast milk in 100-1000-fold higher concentrations compared to cow, goat or sheep. HMOs are one of the most complex naturally occurring carbohydrate structures and the reason why breast milk is so important for infant nutrition. They act as important prebiotics, promoting the growth of beneficial bacteria in the infant’s gut, stimulate a healthy immune system and protect directly against various pathogens by preventing them from binding to epithelial cell linings in the baby’s gut. Furthermore, HMOs contribute to brain development and have anti-inflammatory properties. The production of HMOs, however, has so far been very challenging due to their structural complexity and the intricate enzymatic process required for their synthesis leaving only purification from human milk as an economically viable source.