The ACP is the American College of Physicians which is the largest society of internists in the world. Fellows of ACP are a distinguished group of doctors dedicated to continuing education in the medical practice, teaching, or research. Fellowship is an honorary designation given to recognized ongoing individual service and contributions to the practice of medicine. Fellowship in ACP is a mark of distinction. It says that your doctor has made special efforts to be a better doctor. Ultimately, it says your doctor cares about delivering high-quality health care.