Iron is an essential element required by cells and has been described as a key player in ferroptosis . Ferritin operates as a fundamental iron storage protein in cells forming multimeric assemblies with crystalline iron cores . We discuss the latest findings on ferritin structure and activity and its link to cell metabolism and ferroptosis . The chemistry of iron, including its oxidations states, is important for its biological functions, its reactivity and the biology of ferritin . Ferritin can be localized in different cellular compartments and secreted by cells with a variety of functions depending on its spatial context . Here, we discuss how cellular ferritin localization is tightly linked to its function in a tissue-specific manner, and how impairment of iron homeostasis is implicated in diseases including cancer and COVID-19 . Ferritin is a potential biomarker and we discuss latest research where it has been employed for imaging purposes and drug delivery.