An allopathic (M.D.) and an osteopathic (D.O.) physician are alike in many ways. Both complete four years of basic medical education, and typically have a four-year undergraduate degree with an emphasis on scientific courses. They may select to practice in a specialty area of medicine after completing a residency program, and must pass comparable state licensing examinations. D.O.'s receive extra training in the musculoskeletal system, the body's interconnected system of nerves, muscles and bones as osteopathic physicians seek to understand the interrelationship between these systems and the ways an injury or illness in one part of your body affects another. The Arizona Osteopathic Board of Examiners in Medicine and Surgery licenses and regulates osteopathic physicians.