Leptin was originally described for its role in obesity and energy homeostasis. This book focuses on the biosynthesis, functions and overall clinical significance of leptin. Leptin's association to Alzheimer's diseases and other cognitive disorders is discussed along with the leptin-renal axis; the relationship of leptin and melanoma; the inhibition of oncogenic effects of leptin by cAMP elevation in triple negative breast cancer cells; the leptin regulation of intestinal nutrients absorption; the implications of leptin in male reproductive function; the role of leptin in early life metabolism and its physiological, pathological, and potential therapeutic implications; the skeletal effects of leptin; the physiological roles of leptin in oral and maxillofacial region; the respiratory responses to microinjectons of leptin; and leptin as a reproductive modulator.