The simple answer is that both an MD (Doctor of Medicine) and a DO (Doctor of Osteopathic Medicine) are doctors licensed to practice in the United States. They are similarly educated and certified, but there are differences in their training and philosophy of patient care.

A Physician Assistant is a healthcare professional who practices medicine as a part of a healthcare team with collaborating physicians and other providers. In the United States, PAs are nationally certified and state licensed to practice medicine.

A Nurse Practitioner (NP) is a registered nurse (RN) with advanced training in diagnosing and treating illness. Nurse Practitioners prescribe medications, treat illness, and administer physical exams. NPs differ from physicians in that they focus on prevention, wellness, and education. NPs specialize in providing all encompassing individualized care. Most NPs specialize in particular areas of health care. Many NPs work in primary & acute care settings.