Ferroptosis is a nonapoptotic form of cell death characterized by lethal membrane lipid peroxidation. This mechanism was first characterized in cancer cells well over a decade ago, and there is much enthusiasm for the concept that certain cancers may be treated by inducing ferroptosis. However, therapies that engage ferroptosis have yet to enter clinical testing. In this Review, we highlight the gap between our rapidly expanding knowledge of the ferroptosis mechanism and its translation into cancer therapies. We discuss the known challenges that may be slowing ferroptosis therapies from reaching the clinic.