A fellowship is the period of medical training, in the United States and Canada, that a physician, dentist, or veterinarian may undertake after completing a specialty training program (residency).
Fellows are capable of acting as an attending physician or a consultant physician in the specialist field in which they were trained, such as internal medicine or pediatrics.
After completing a fellowship in the relevant sub-specialty, the physician is permitted to practice without direct supervision by other physicians in that sub-specialty, such as cardiology or oncology.
In the US, the majority of fellowships are accredited by the Accreditation Council for Graduate Medical Education ("ACGME") or, to a lesser extent, the American Board of Physician Specialties in select states.
There are fellowship programs that are not ACGME accredited, yet are well received, given the importance of being a Board-Certified Physician in a primary specialty, where a Fellowship is often more based on demand and research productivity.