Internal medicine, also known as general internal medicine in Commonwealth nations, is a medical specialty for medical doctors focused on the prevention, diagnosis, and treatment of internal diseases in adults. Medical practitioners of internal medicine are referred to as internists, or physicians in Commonwealth nations. Internists possess specialized skills in managing patients with undifferentiated or multi-system disease processes. They provide care to both hospitalized (inpatient) and ambulatory (outpatient) patients and often contribute significantly to teaching and research. Internists are qualified physicians who have undergone postgraduate training in internal medicine, and should not be confused with "interns", a term commonly used for a medical doctor who has obtained a medical degree but does not yet have a license to practice medicine unsupervised.

A primary care physician (PCP) is a physician who provides both the first contact for a person with an undiagnosed health concern as well as continuing care of varied medical conditions, not limited by cause, organ system, or diagnosis. The term is primarily used in the United States. In the past, the equivalent term was 'general practitioner' in the US; however in the United Kingdom and other countries the term general practitioner is still used. With the advent of nurses as PCPs, the term PCP has also been expanded to denote primary care providers.