Hepatitis E virus (HEV) represents the main aetiological agent of enteric non-A hepatitis and is the only member of a new virus, Hepevirus, belonging to the family of Hepeviridae. HEV is the single most important cause of acute clinical hepatitis among adults in many areas of the developing world, specifically the Indian subcontinent and Southeast Asia, the Middle East and North Africa, where it is a common cause of sporadic and epidemic waterborne outbreaks and results in a high rate of morbidity and death, especially in pregnant women. Once thought of as an infection confined to developing countries, it is now recognized as a geographically widely distributed disease. In low-endemic regions (Western countries), sporadic cases of locally-acquired HEV infection are reported, acquired possibly through zoonotic transmission from pigs, wild boars or deer. In persons with pre-existing chronic liver disease, HEV superinfection can present as acute-on-chronic liver disease. In European countries, chronic infection, which may progress to liver cirrhosis, has been reported among immunosuppressed persons. Two testing vaccines proved to be highly effective in preventing the disease; these vaccines should be of particular use in groups that are at high risk of HEV infection.