The first study of a nationally representative group of US infants reports that more than half of babies are currently introduced to complementary foods, that is, foods or drinks other than breast milk or formula, sooner than they should be. Babies who were never breastfed or breastfed for less than four months were most likely to be introduced to foods too early. These findings emphasize the need to introduce foods at the proper time to get the most benefit from breast milk or formula.