A physician, medical practitioner (British English), medical doctor, or simply doctor is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through the study, diagnosis, prognosis and treatment of disease, injury, and other physical and mental impairments.

Degrees and other qualifications vary widely, but there are some common elements, such as medical ethics requiring that physicians show consideration, compassion, and benevolence for their patients.

[4] This term is at least nine hundred years old in English: physicians and surgeons were once members of separate professions, and traditionally were rivals.

Another term, hospitalist, was introduced in 1996,[7] to describe US specialists in internal medicine who work largely or exclusively in hospitals.

This original use, as distinct from surgeon, is common in most of the world including the United Kingdom and other Commonwealth countries (such as Australia, Bangladesh, India, New Zealand, Pakistan, South Africa, Sri Lanka, and Zimbabwe), as well as in places as diverse as Brazil, Hong Kong, Indonesia, Japan, Ireland, and Taiwan.

All boards of certification now require that physicians demonstrate, by examination, continuing mastery of the core knowledge and skills for a chosen specialty.

Primary care physicians guide patients in preventing disease and detecting health problems early while they are still treatable.

[20] DPM is also available at one Canadian university, namely the Université du Québec à Trois-Rivières; students are typically required to complete an internship in New York prior to obtaining their professional degree.

[24] Biomedicine "formulates the human body and disease in a culturally distinctive pattern",[25] and is a world view learnt by medical students.

Within this tradition, the medical model is a term for the complete "set of procedures in which all doctors are trained",[26] including mental attitudes.

[30] The US National Center for Complementary and Alternative Medicine (NCCAM) classifies complementary and alternative medicine therapies into five categories or domains, including:[31] alternative medical systems, or complete systems of therapy and practice; mind-body interventions, or techniques designed to facilitate the mind's effect on bodily functions and symptoms; biologically based systems including herbalism; and manipulative and body-based methods such as chiropractic and massage therapy.

In considering these alternate traditions that differ from biomedicine (see above), medical anthropologists emphasize that all ways of thinking about health and disease have a significant cultural content, including conventional western medicine.

Some commentators have argued that physicians have duties to serve as role models for the general public in matters of health, for example by not smoking cigarettes.

[35] Physicians do experience exposure to occupational hazards, and there is a well-known aphorism that "doctors make the worst patients".

[36] Causes of death that are shown to be higher in the physician population include suicide among doctors and self-inflicted injury, drug-related causes, traffic accidents, and cerebrovascular and ischaemic heart disease.

This manifests as a long-term stress reaction characterized by poorer quality of care towards patients, emotional exhaustion, a feeling of decreased personal achievement, and others.

Depending on jurisdiction and university, entry may follow directly from secondary school or require pre-requisite undergraduate education.

Programs that require previous undergraduate education (typically a three- or four-year degree, often in science) are usually four or five years in length.

Following the completion of entry-level training, newly graduated medical practitioners are often required to undertake a period of supervised practice before full registration is granted, typically one or two years.

In other jurisdictions, junior medical doctors must undertake generalist (un-streamed) training for one or more years before commencing specialization.

Synonyms in use elsewhere include colegiación in Spain, ishi menkyo in Japan, autorisasjon in Norway, Approbation in Germany, and άδεια εργασίας in Greece.

[41] After graduating from a first-professional school, physicians who wish to practice in the US usually take standardized exams, such as the USMLE for a Doctor in Medicine.

[46] In Europe, as of 2009 the health systems are governed according to various national laws, and can also vary according to regional differences similar to the United States.