Human milk remains the gold standard for infant nutrition. As a nutritional source, it shows a relatively large degree of both intra- and inter-individual variability in composition. It can be said that the more we learn about the unique compositional qualities of human milk, the more there is to learn. Although it is unreasonable to expect any artificial formula to duplicate this mammary gland secretion, this has remained an elusive goal of nutritionists and formula companies throughout the 20th century. Infant formulas have changed substantially since the burgeoning of the modern formula industry in the 1950s. Many of these changes, such as the additions of iron, vitamin D, and perhaps vitamin K, addressed specific well-documented deficiencies and actually moved infant formula away from the composition of human milk. However, the majority of the changes made in recent years have been attempts to bring formulas closer in composition to human milk. The additions of taurine and carnitine, further reductions in sodium content, and increases in the percent of whey protein, though advantageous theoretically, have remained of questionable benefit when subjected to rigorous scientific methods. Much of the supporting research for formula modifications is sponsored by the formula industry, the results of which are then widely advertised in circulars aimed at practitioners involved in the care of infants.