Human milk oligosaccharides, often known as HMOs, are the third most prevalent solid component found in human milk. Due to secretor status, race, geographic location, season, maternal nutrition and weight, gestational age, and delivery technique, HMO levels and distribution vary greatly across women. HMOs have been shown to have a variety of functional roles in the development of infants in recent studies. Because HMOs are not digested by the infants, they act as metabolic substrates for certain bacteria, helping to establish the infant's gut microbiota. By encouraging the growth of advantageous intestinal bacteria, these sugars function as prebiotics and produce short-chain fatty acids (SCFAs), which are essential for gut health. HMOs can also specifically reduce harmful microbe and virus binding to the gut epithelium, preventing illness. They can also directly regulate host-epithelial immunity. HMO addition to infant formula is safe and promotes healthy development, infection prevention, and microbiota. Current infant formulae frequently contain oligosaccharides (OSs) that differ structurally from those found in human milk, making it unlikely that they would reproduce the unique effects of HMOs. However, there is a growing trend of manufacturing OSs similar to those found in human milk. There is insufficient information available to compare the effects of HMOs with non-human OSs, hence it is unknown if HMOs have any further therapeutic advantages. Better knowledge of how the human mammary gland synthesizes HMOs could direct the development of technologies that yield a broad variety of complex HMOs with OSs compositions that closely mimic human milk. This review discusses HMOs' broad and complicated nature, as well as their critical role in newborn health. The large variance in HMO composition among mothers and the contributing factors are investigated. The most recent technology developments that allow large-scale investigations on HMO composition and its impact on infant health outcomes are highlighted. Furthermore, HMOs' multifunctional roles in biological process such as infection prevention, brain development, and gut microbiota and immune response regulation are investigated. The structural distinctions between HMOs and other mammalian OSs in infant formulae are discussed, with a focus on the trend towards producing more precise replicas of HMOs found in human milk.