Doctor of Osteopathic Medicine (D.O. or DO) is a professional doctoral degree for physicians and surgeons offered by medical schools in the United States. Holders of the D.O. degree have attained the ability to become licensed as osteopathic physicians who have equivalent rights, privileges, and responsibilities as physicians with a Doctor of Medicine degree (M.D.). D.O. physicians are licensed to practice the full scope of medicine and surgery in 65 countries, including all 50 states in the US, and make up 7 percent of the total U.S. physician population. In 2013, there were 87,300 osteopathic physicians in the United States. Currently, there are 30 medical schools with 42 locations throughout the United States that offer the D.O. degree, and 141 medical schools that offer the M.D. degree. As of 2013, 22% of graduating medical students in the United States were D.O. students, and this percentage increases every year. The curricula at osteopathic medical schools are very similar to those at M.D.-granting medical schools. Four years in total length, the first two years of medical school focus on the biomedical and clinical sciences, followed by two years of core clinical training in the clinical specialties. Upon leaving medical school, D.O. graduates may enter internship or residency training programs, which may be followed by fellowship training. Many D.O. graduates attend the same graduate medical education programs as their M.D. counterparts, and then take M.D. specialty board exams, while other D.O. graduates enter osteopathic programs and take D.O. specialty board examinations. One notable difference between D.O. and M.D. training is that D.O. training adds 300–500 hours studying philosophically based techniques for hands-on manipulation of the human musculoskeletal system. These techniques, known as osteopathic manipulative medicine (OMM), have been criticized as “pseudoscientific”.