Iron deficiency anemia is the most common micronutrient deficiency worldwide and infants constitute a risk group due to their high iron requirements. Iron is critical for brain development, and case control studies have shown a consistent association between iron deficiency anemia in infancy and poor neurodevelopment, suggesting that it is important to prevent iron deficiency anemia in infants. However, it is also important to avoid excessive iron intakes which may have adverse effects on growth. Due to redistribution of iron from hemoglobin to iron stores, healthy, term, normal birth weight infants are virtually self-sufficient with regard to iron during the first 6 months of life. After that age, iron becomes a critical nutrient. The estimated daily iron requirements at the age of 6–12 months (0.9–1.3 mg/kg body weight) are higher than during any other period of life. Exclusively breast-fed infants normally do not need additional iron until 6 months of life. Formula-fed infants should receive iron-fortified formula. Low birth weight infants should receive additional iron supplements from an early age. From 6 months of age, all infants should receive a sufficient intake of iron-rich (complementary) foods, which may be meat products or iron-fortified foods. The estimations of iron requirements in infants have a weak evidence base and current European and American recommendations for infants differ significantly. To further clarify iron requirements in infants, there is clearly a need for randomized, controlled trials assessing the effects of different iron intake on anemia, neurodevelopment, and other health outcomes.