Fatigue can have a major impact on an individual‎'‎s performance and well‎-being‎,‎ yet is poorly understood‎,‎ even within the scientific community‎.‎ There is no developed theory of its origins or functions‎,‎ and different types of fatigue ‎(‎mental‎,‎ physical‎,‎ sleepiness‎)‎ are routinely confused‎.‎ The widespread interpretation of fatigue as a negative consequence of work may be true only for externally imposed goals‎;‎ meaningful or self‎-initiated work is rarely tiring and often invigorating‎.‎ In the first book dedicated to the systematic treatment of fatigue for over sixty years‎,‎ Robert Hockey examines its many aspects ‎- social history‎,‎ neuroscience‎,‎ energetics‎,‎ exercise physiology‎,‎ sleep and clinical implications ‎- and develops a new motivational control theory‎,‎ in which fatigue is treated as an emotion having a fundamental adaptive role in the management of goals‎.‎ He then uses this new perspective to explore the role of fatigue in relation to individual motivation‎,‎ working life and well‎-being‎.‎