A physician, medical practitioner, doctor of medicine, or medical doctor practices medicine, and is concerned with maintaining or restoring human health through the study, diagnosis, and treatment of disease and injury. This is accomplished through a detailed knowledge of anatomy, physiology, diseases and treatment — the science of medicine — and its applied practice — the art or craft of medicine.

The word physician φύσις (physis) and its derived adjective physikos, meaning "nature" and "natural". From this, amongst other derivatives came the Vulgar Latin physicus, which meant a medical practitioner. After the Norman Conquest, the word entered Middle English via Old French fisicien, as early as 1100. Originally, physician meant a practitioner of physic (pronounced with a hard C). This archaic noun had entered Middle English by 1300 (via Old French fisique). Physic meant the art or science of treatment with drugs or medications (as opposed to surgery), and was later used both as a verb and also to describe the medications themselves.

In English, there have been many synonyms for physician, both old and new, with some semantic variation. The noun phrase medical practitioner is perhaps the most widely understood and neutral synonym. Medical practitioner is lengthy but inclusive: it covers both medical specialists and general practitioners (family physician, family practitioner), and historically would include physicians (in the narrow sense), surgeons or apothecaries. In England, apothecaries historically included those who now would be called general practitioners and pharmacists.