Depression frequently starts during adolescence, and fatigue is one of the nine main symptoms. Despite indications that many adolescents with depression also report problematic fatigue, it is often not routinely addressed or treated in public healthcare services for children and adolescents with mental health difficulties. Minimal research has been conducted in this area, so there are many unanswered questions as to the importance of fatigue in adolescent depression, including how it is experienced, identified, and treated. The aim of my PhD is to begin addressing this gap in our knowledge by exploring fatigue as a common symptom in adolescent depression.