This book contains seven chapters that detail leptin and its role in health and disease. Chapter One discusses many features of leptin and emphasizes the significance of future research to better understand leptin's involvement in neurological and behavioral disease causes and therapy. Chapter Two details the role of leptin as a biochemical marker. Chapter Three presents the consequences of hyperleptinemia caused by high leptin serum levels and leptin receptor resistance in obesity on renal, cardiac, vascular, and sympathetic nervous system function. The objective of Chapter Four is to shed light on the reproductive functions of leptin and its role in altered reproductive physiology. Chapter Five discusses the role of leptin in the pathogenesis and progression of diabetes and diabetic complications. Chapter Six summarizes the current understanding of the role of leptin in nutrition and cancer. Lastly, Chapter Seven provides a comprehensive review on the importance of leptin during different pathological conditions.