This report delves into the realm of health psychology, examining the interplay of psychological and behavioral processes in health, illness, and healthcare. It begins by comparing different theories of lifespan development, including Erikson's psychosocial theory and Freud's psychosexual theory, highlighting their core concepts and differences. The report then explains behavioral, cognitive, psychodynamic, and humanist theories, demonstrating their relevance to various life stages. Furthermore, it explores the impact of social and biological factors on human behavior, addressing the nature versus nurture debate. The importance of social roles in health and social care is analyzed, emphasizing the role of social workers. The report includes application of psychological theories in relation to a case study and analyzes psychological theories that inform understanding of mental disorders and behavior disturbance. Finally, it examines psychological principles affecting behavior change and theories that enhance understanding of relationships in health and social care, providing a comprehensive overview of the subject.