Fatigue is a prevalent problem and adequate treatment is challenging because many conditions, disorders, medications, and lifestyle factors can cause fatigue. The Scientific Basis of Fatigue combines evidence-based research and clinical treatment protocols to provide a comprehensive reference to fatigue. This book is divided into seven distinct sections, starting with an introduction section defining the distinctions between physical and mental fatigue. The second and third sections detail the various conditions in both physical and mental fatigue including COVID, Parkinson disease, and depression. The next section reviews the current research on molecular and cellular aspects and models of fatigue. The final two sections review options for diagnosis and treatments for fatigue and provides a detailed resource section for further review.