Occupational medicine is the branch of clinical medicine most active in the field of occupational health. Occupational health physicians work closely with the occupational health team which consists of Occupational Health Nursing Professional, Industrial Hygienists, Biostaticians, Public Health Specialists, and Biomedical Engineers (namely those specializing in Ergonomics). In the United States it is one of the three medical specialties (also including aerospace medicine and public health and general preventive medicine) encompassed by the American Board of Medical Specialties recognized specialty of preventive medicine. Its principal role is the provision of health advice to organisations and individuals to ensure that the highest standards of health and safety at work can be achieved and maintained. Occupational physicians must have a wide knowledge of clinical medicine and be competent in a number of important areas.