Iron is essential for cells to function, but excess iron can damage cells. Accordingly, cells have sophisticated molecular mechanisms to constantly sense and adjust iron levels. Disorders of cellular iron metabolism affect, by some estimates, more than a third of the world’s population. In addition to well-known disorders like anemia, caused by overall insufficient levels of iron in the human body, iron deficiency can impair brain function in the young and reduce muscle strength in adults. Iron may be dysregulated at the level of individual cells in neurological disorders such as Parkinson’s disease, and disordered iron metabolism contributes to congenital conditions such as Friedrich’s ataxia.