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, PA's are nationally certified and state licensed to practice medicine. PAs are concerned with preventing and treating human illness and injury by providing a broad range of health care services with a collaborating physician. Their scope of practice can vary according to jurisdiction and healthcare setting, some will require a license. Accordingly, their work may include conducting physical exams, ordering and interpreting tests, diagnosing illnesses, developing treatment plans, performing procedures, prescribing medications, advising on preventive health care, and assisting in surgery.