Breast milk is a dynamic fluid with compositional changes occurring throughout the period of lactation. Some of these changes in nutrient concentrations reflect the successively slowing growth rate and developmental changes in metabolic requirements that infants undergo during the first year of life. Infant formula, in contrast, has a static composition, intended to meet the nutritional requirements of infants from birth to 6 or 12 months of age. To better fit the metabolic needs of infants and to avoid nutrient limitations or excesses, we suggest that infant formulas should change in composition with the age of the infant, that is, different formulas are created/used for different ages during the first year of life. We propose that specific formulas for 0 to 3 months (stage 1), 3 to 6 months (stage 2), and 6 to 12 months (stage 3) of age may be nutritionally and physiologically advantageous to infants. Although this initially may impose some difficult practical/conceptual issues, we believe that this staging concept would improve nutrition of formula-fed infants and, ultimately, improve outcomes and make their performance more similar to that of breast-fed infants.