This book delves into the fundamental principles and theories of three interconnected fields: health psychology, neuropsychology, and behavioral therapy. It explores how psychological, behavioral, and cognitive factors influence physical health and illness. The text also examines the intricate relationship between brain function and behavior, providing crucial insights into neurological disorders. Furthermore, it comprehensively covers various behavioral therapy techniques used for treatment and intervention. Authored by Prof. Dr. Saleh Hassan Al-Daheri, this guide is essential for students, researchers, and practitioners seeking a deep understanding of these critical areas of modern psychology, bridging theory with practical application.