Certified specialists are doctors who have advanced education, clinical training, and certification in a specific field. A sub-specialist is a doctor who is trained or certified as a specialist and then receives additional training in a specific area (sub-specialty).

A doctor becomes certified by completing training in a specialty area and passing an exam. To be certified, the doctor must complete the education required to get an MD (medical doctor) or DO (doctor of osteopathic medicine) degree, complete 3 to 7 years of training in a residency program in the specialty field, and pass a written test given by the Royal College of Physicians and Surgeons of Canada. Many specialty boards also require doctors to pass an oral test.