Fatigue is one of the most common and debilitating symptoms experienced by individuals with long COVID. This chapter provides an overview of the current state of knowledge on the diagnosis and treatment of fatigue in long COVID patients. Various objective and subjective measurement tools used to assess the severity and impact of fatigue are discussed, including cardiopulmonary exercise testing, accelerometry, neuroimaging, biomarkers, and self-report questionnaires such as the Fatigue Severity Scale and Chalder Fatigue Scale. The chapter also explores a range of treatment options, including lifestyle modifications, pharmacologic and nonpharmacologic interventions, and emerging therapies such as cannabis and noninvasive brain stimulation. The importance of personalized treatment plans and multidisciplinary care is emphasized throughout the chapter. As the understanding of long COVID fatigue continues to evolve, further research is needed to refine diagnostic criteria, validate assessment tools, and establish the efficacy and safety of various treatment approaches. This chapter serves as a comprehensive resource for healthcare providers, researchers, and patients seeking to better understand and manage this complex and debilitating symptom of long COVID.