Iron deficiency anemia is the most common nutritional deficiency worldwide, and the most susceptible groups are infants, preschoolers, women of childbearing age, and pregnant women. It is therefore essential to understand the mechanisms of regulation of iron uptake, transport, and absorption at the cellular level, particularly in enterocytes, and to identify blood biomarkers that allow the evaluation of iron status. This review describes how iron absorption is regulated by intestinal epithelial cells, the main proteins involved (iron transporters, oxidoreductases, storage proteins), and the main blood biomarkers of iron metabolism.