Iron deficiency is often cited as the most common nutritional deficiency in the world and is a leading cause of both mortality and disability. Iron deficiency can impair cognitive development, immunity, work capacity and childbirth. However, only a small fraction of dietary iron is absorbed and utilized, and it is substantially influenced by the chemical form and by other dietary components ingested at the same time. As a result, information on iron bioavailability from foods, diets, and iron fortificants is crucial in the development of interventions based on food fortification and dietary diversification. Isotopic techniques have been instrumental in determining iron bioavailability from iron compounds used in food fortification programs and for identifying enhancers and inhibitors of iron absorption to improve diets. The IAEA provides information on the theoretical background and practical application of state of the art methodology for iron bioavailability assessment using stable isotopes.