Physicians are involved in the prevention, diagnosis, and treatment of disease. There are two paths to becoming a physician. Allopathic medical school leads to an M.D. (medical doctor) and osteopathic medical school leads to a D.O. (doctor of osteopathic medicine). Both M.D.’s and D.O.’s are licensed to diagnose, prescribe, treat, and perform surgery in all 50 states and the District of Columbia.