Internal medicine specialists, also known as general internal medicine specialists or general medicine physicians in Commonwealth countries,  are specialist physicians trained to manage particularly complex or multi-system disease conditions that single-organ-disease specialists may not be trained to deal with. They may be asked to tackle undifferentiated presentations that cannot be easily fitted within the expertise of a single-organ specialty,  such as dyspnoea, fatigue, weight loss, chest pain, confusion or change in conscious state. They may manage serious acute illnesses that affect multiple organ systems at the same time in a single patient, and they may manage multiple chronic diseases or “comorbidities” that a single patient may have.

General internal medicine specialists do not provide necessarily less expertise than single-organ specialists, rather, they are trained for a specific role of caring for patients with multiple simultaneous problems or complex comorbidities.

Perhaps because it is complex to explain treatment of diseases that are not localised to a single-organ, there has been confusion about the meaning of internal medicine and the role of an “internist.” Internists are qualified physicians with postgraduate training in internal medicine and should not be confused with “interns”, who are doctors in their first year of residency training. Although internists may act as primary care physicians, they are not “family physicians,” “family practitioners,” or “general practitioners,” whose training is not solely concentrated on adults and may include surgery, obstetrics, and pediatrics. The American College of Physicians defines internists as “physicians who specialize in the prevention, detection and treatment of illnesses in adults”.

Internal medicine physicians have practiced both in clinics and in hospitals, often in the same day. Pressures on time have led to many internal medicine physicians to choose one practice setting, who may choose to practice only in the hospital, as a “hospitalist”, or only in an outpatient clinic, as a primary care physician.