Hepatology is essentially the field of liver disease. The liver is the body's largest organ and hepatology is a large field. It includes, but is not limited to, the study of acute and chronic hepatitis, viral hepatitis, cirrhosis, genetic and metabolic liver diseases and their complications, liver cancer, liver transplantation, drug metabolism (which depends largely upon the liver), and immunology as it pertains to the liver. Historically, hepatology grew out of gastroenterology and became a subfield of it, although today it has become an emerging freestanding medical specialty.