Doctors

Doctors have the most demanding education and training requirements. They typically need a bachelor's degree followed by a degree from a four-year medical school and, depending on their specialty, three to seven years of additional training.

Credentials for doctors:

• M.D.: Doctor of medicine
• D.O.: Doctor of osteopathic medicine; equivalent to an M.D.
• M.B.B.S.: Bachelor of medicine, bachelor of surgery; an international medical degree equivalent to an M.D. in the U.S. system (also abbreviated as M.B., Ch.B.; M.B., B.Ch.; M.B., B.Chir.)

Not every provider with a doctorate degree is a medical doctor. For example, optometrists and pharmacists have graduate degrees and specialized training but don't attend medical school.