FATIGUE IS SOMETHING almost all children and teens experience while being treated for cancer. For a small percentage of survivors, however, the profound tiredness lasts long after treatment. People with fatigue have little energy and feel emotionally, physically, and mentally tired. Fatigue may have an identifiable physical cause, or it may remain an elusive—but life-altering—late effect of treatment. This chapter describes fatigue, its causes, and its treatment. It also includes the voices of many survivors who live with and cope with chronic fatigue.