This chapter presents the epidemiology, clinical features, pathology, and etiology of the enterically transmitted form. Following the identification of the hepatitis A and B viruses, it became possible to test large panels of sera which had been collected from patients with acute viral hepatitis in different parts of the world and determine the prevalence of these infections. In retrospect the first well documented outbreak of non-A, non-B hepatitis (HNANB) appears to have taken place in New Delhi, India in 1955 to 1956. The outbreak was confirmed as HNANB on the basis of typical clinical, biochemical, and histological data supported by negative tests for recent infection with Hepatitis A virus or Hepatitis B virus. This epidemic has some features which distinguish it from other outbreaks in the Indian subcontinent. The occurrence of a large outbreak of hepatitis A was recognized to be unusual and interpreted as being due to a different strain of virus.