Osteopenia, rickets, and fractures from nutrient deficiencies can occur during infancy, particularly in preterm infants. Bone mass accretion during the first year of life is equal to or greater than that achieved at any other stage of life, including adolescence. Optimizing calcium and bone status during infancy can have immediate benefits in maintaining calcium homeostasis and preventing disturbances in bone mineralization and can provide long-term benefits by helping infants to later reach their maximum genetic potential for peak bone mass, a prerequisite for the prevention of osteoporosis and its complications. Dietary calcium requirements during infancy generally reflect the need to achieve normal growth and bone mineralization because 99 percent of total body calcium is present in the skeleton. Knowledge of physiologic factors that determine infant calcium requirements and the bioavailability of calcium from various dietary sources is important to ensuring bone health during infancy. Also key are the practical issues related to optimizing calcium nutriture in infants born at term and prematurely.