An anesthesiologist (American English) or anaesthetist (British English) is a physician trained in anesthesia and perioperative medicine.

Terminology varies between countries. In the United States, the term anesthesiologist refers to a physician who has completed an accredited residency program in anesthesiology after medical school training, while the term anesthetist is used for nurse anesthesia providers who have undergone specialized training in administering anesthesia under the supervision of a physician. By contrast, in the UK, most former Commonwealth countries and in Europe, the word anaesthetist is used to refer only to physicians, while their assistants may be termed anaesthetic nurses, anaesthetic technicians, operating department practitioners or physician associates depending on local practice.