Commercially available infant formulas serve as the best alternative to human milk when breastfeeding is not possible. Infant formulas are designed specifically to mimic the composition of human milk or the functional aspects of human milk feeding. This review highlights the issues related to the composition of infant formulas. The most hotly debated issue currently is whether to add long-chain polyunsaturated fatty acids to infant formulas. Other controversial topics include the safety and efficacy of soy-based protein formulas, protein quantity and quality as they relate to the infant's nutritional needs and feeding tolerance, and the replacement of lactose with other carbohydrate sources for specialized infant formulas. Recent modifications in the fat blend of infant formulas have led to improved fat digestibility. However, the full spectrum of benefits associated with the addition of nucleotides awaits further study. Modifications to infant formulas are made when the preponderance of scientific evidence suggests that the compositional change will better meet the nutritional needs of the infant.