Progress in research on human lactation and breast milk has advanced our knowledge about the significance of breast milk for the recipient infant and the effects of various components on long-term outcomes. Recent findings have expanded our knowledge in this area. Several growth factors and cytokines are present in breast milk and their capacity to persist in the infant gut and exert their activities is likely to affect maturation of immune function, possibly affecting the development of oral tolerance. A proper balance of polyunsaturated fatty acids (n-3/n-6 ratio) may also be of significance for allergy prevention in children, emphasizing the need for the mother to achieve a balance of these fatty acids in her diet. The recent findings that specific strains of bacteria are present in breast milk and act as probiotics in the early colonization of the infant gut and that human milk oligosaccharides are specific substrates for these probiotic strains may not only affect the defense against pathogens, but also affect energy utilization and development of obesity. Previously neglected milk fat globule membranes contain several components involved in protection against infection and may be an additional arm in the multifaceted shield that breastfed infants have developed against bacterial and viral antagonists. All these findings have implications for development of improved infant formulae.