The past two decades have seen a series of breakthroughs in the understanding, prevention, and treatment of viral hepatitis. Developed countries have an increasing number of adults who are susceptible to hepatitis A virus (HAV) infection. The licensing of an effective hepatitis A vaccine presents new opportunities for prevention in persons at risk for HAV infection. Hepatitis B virus (HBV) infection is an important cause of chronic liver disease throughout the world. Although a hepatitis B vaccine has been available in the United States for 15 years, recommendations for its use have undergone changes. Report of the discovery of hepatitis C virus (HCV) in 1989 has led to a marked decrease in the risk of transfusion-transmitted viral hepatitis. HCV infection, however, remains a common cause of chronic liver disease, and a hepatitis C vaccine is needed to prevent the consequences of this disease. Basic research into the hepatitis C viral genome has elucidated some of the obstacles in the way of hepatitis C vaccine development.