Publisher Summary Viral hepatitis is defined as an episode of hepatitis caused by a virus for which the liver is the primary target. This definition excludes viruses that cause inflammation of the liver as part of a generalized infection, such as yellow fever, varicella-zoster, herpes simplex, cytomegalo-, coxsackie, Epstein-Barr, and rubella viruses. Currently, at least five different forms of acute viral hepatitis have been identified: Hepatitis A, B, C, D, and E. The etiological agents of hepatitis A, B, and D are well characterized, whereas the agents responsible for hepatitis C and E have only been described recently and are not well characterized. Hepatitis E (formerly known as enterically transmitted hepatitis non-A non-B) was recognized to be distinct from hepatitis A after paired serum samples from individuals involved in some epidemics of water-borne hepatitis showed no evidence of recent infection with hepatitis A.