Iron is a trace element that is vital for life. It is a component of innumerable hemoproteins and many essential non-heme iron proteins that are involved in oxygen binding and metabolism and electron transfer. Nevertheless, iron can also be toxic to cells as it catalyses the production of oxygen radicals. Iron uptake, transport, storage and utilization are therefore strictly regulated to meet the body's iron needs and to avoid its potential toxicity. Any imbalance in iron homeostasis may lead to the development of pathological conditions associated with either iron overload or iron deficiency. In this paper, we review the current understanding of iron biology with a focus on erythroid iron demand. In addition, we will discuss molecular pathophysiology with implications for novel therapies of selected hereditary defects of iron homeostasis.