is also a major contributor to the prevention-focused field of behavioral health and the treatment-oriented field of behavioral medicine. Clinical practice includes education, the techniques of behavior change, and psychotherapy. In some countries, a clinical health psychologist, with additional training, can become a medical psychologist and, thereby, obtain prescription privileges. Public health psychology (PHP) PHP is population-oriented. A major aim of PHP is to investigate potential causal links between psychosocial factors and health at the population level. Public health psychologists present research results to educators, policy makers, and health care providers in order to promote better public health. PHP is allied to other public health disciplines including epidemiology, nutrition, genetics and biostatistics. Some PHP interventions are targeted toward at-risk population groups (e.g., undereducated, single pregnant women who smoke) and not the population as a whole (e.g., all pregnant women). Community health psychology (CoHP) CoHP investigates community factors that contribute to the health and well-being of individuals who live in communities. CoHP also develops community-level interventions that are designed to combat disease and promote physical and mental health. The community often serves as the level of analysis, and is frequently sought as a partner in health-related interventions. Critical health psychology (CrHP) CrHP is concerned with the distribution of power and the impact of power differentials on health experience and behavior, health care systems, and health policy. CrHP prioritizes social justice and the universal right to health for people of all races, genders, ages, and socioeconomic positions. A major concern is health inequalities. The critical health psychologist is an agent of change, not simply an analyst or cataloger. A leading organization in this area is the International Society of Critical Health Psychology. Occupational health psychology Pickren and Degni and Sanderson observed that in Europe and North America, occupational health psychology (OHP) emerged as a specialty with its own organizations. The authors noted that OHP owes some of that emergence to health psychology as well as other disciplines (e.g., i/o psychology, occupational medicine). Sanderson underlined examples in which OHP aligns with health psychology, including Adkins's research. Adkins documented the application of behavioral principles to improve working conditions, mitigate job stress, and improve worker health in a complex organization. Origins and development Health psychology developed in different forms in different societies. Psychological factors in health had been studied since the early 20th century by disciplines such as psychosomatic medicine and later behavioral medicine, but