The growth pattern of formula-fed infants is quite different from that of breastfed infants. There may be several reasons for this difference, ranging from different endocrine responses to feeding and the presence of growth factors in breast milk to different control of food intake, but it is highly likely that differences in nutrient composition of the food (breast milk or formula) have major effects on growth. In most countries infant formula is used more or less exclusively up to 6 months of age and as part of the diet up to 12 months of age and during this period its composition remains the same. In striking contrast, the nutrient composition of breast milk changes during lactation, most dramatically during early lactation, but with pronounced differences throughout lactation for many nutrients. It is a goal that the performance of formulafed infants should be as similar to that of breastfed infants as possible, and attempts have been made to modify the composition of infant formula to achieve this goal. However, there has been no systematic attempt to gradually change the composition of infant formula in a manner similar to the changing pattern of breast milk. This represents a technical and nutritional challenge, but is now possible.