A gastroenterologist is a healthcare professional who has been educated and trained to treat patients who are experiencing health problems or have diseases that affect the gastrointestinal tract and liver. They also diagnose and treat diseases that affect the esophagus, stomach, small intestine, colon, rectum, pancreas, gallbladder, bile ducts, and liver.

A hospitalist is a doctor who works only in a hospital setting. Hospitalists care for patients who are staying in the hospital to recover from an illness or a surgery. Most hospitalists are also internists, and many primary care doctors are hospitalists. Some of them also work in subspecialties or have work in other areas early in their careers. Hospitalists coordinate care for patients admitted in the hospital. They play the role of Primary care doctors in hospital settings.

An internist or Internal Medicine doctor is someone who specializes in diagnosing and treating illnesses, diseases, and health problems. Most internists are also primary care doctors and treat patients on a regular basis. They can diagnose and treat common illnesses or more serious problems. Most people see an internist regularly. Those with chronic illnesses may do so on a monthly or even weekly basis. Internists are the most common types of doctors.