High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! A physician assistant (PA) is a healthcare professional licensed to practice medicine with supervision of a licensed physician. A physician assistant is concerned with preventing, maintaining, and treating human illness and injury by providing a broad range of health care services that are traditionally performed by a physician. Physician assistants conduct physical exams, diagnose and treat illnesses, order and interpret tests, counsel on preventive health care, assist in surgery, and write prescriptions.