Hepatitis is an important worldwide cause of acute and chronic liver disease. Etiologies include toxins, drugs, and viruses. Viral hepatitis alone afflicts over half a billion people around the world. Among the responsible viruses are hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), and hepatitis D virus (HDV). Complications include fulminant liver failure, cirrhosis and hepatocellular carcinoma (HCC). Current therapies are inadequate for most infected patients, and the clinical needs are increasing.