An intensivist, also known as a critical care doctor, is a medical practitioner who specializes in the care of critically ill patients, most often in the intensive care unit (ICU).

Intensivists can be internists or internal medicine sub-specialists (most often pulmonologists), anesthesiologists, emergency medicine physicians, pediatricians (including neonatologists), or surgeons who have completed a fellowship in critical care medicine. The intensivist must be competent not only in a broad spectrum of conditions among critically ill patients but also with the technical procedures and equipment (i.e. mechanical ventilators) used in the intensive care setting.