For more than 150 years, people have been searching for a substitute food similar to breast milk to improve the health of non-breastfed infants. Human milk oligosaccharides (so-called HMOs), complex sugars that make up the third largest fraction of milk by volume, have also received considerable attention, particularly as a factor influencing bacterial colonization of the infant gut. More and more functions are being discussed for the numerous HMOs, of which well over 100 different structures have been identified. They are considered anti-inflammatory, anti-infective and are even said to positively influence brain development. For some years now, it has been possible to produce individual representatives of the HMOs synthetically in larger quantities, making clinical studies possible for the first time. They are also already being added to infant milk formula. However, since the individual composition of HMOs is very different, the lecture will discuss whether and to what extent the complex system of these structures and their interactions with various microorganisms in humans and their immune systems can be generally imitated for all infants.