Infection with hepatitis B virus (HBV) is the most common cause of chronic hepatitis and hepatocellular carcinoma in the world today despite the availability of an effective vaccine and antiviral therapies. The virus causes both acute and chronic infections. It is estimated 254 million in the world today are chronically infected with HBV. The epidemiology of this viral infection has revealed effective strategies for prevention and control that may lead to future reductions in the burden of disease, and even global elimination. Hepatitis D virus, also known as delta virus, is a defective virus that cannot establish or maintain infection except in the presence of HBV. While the global impact of HDV infection is less than that of HBV alone, its prevention and control represent unique challenges due to its unusual characteristics.