Hepatitis delta virus is a defective virus and found in patients expressing HBsAg. It is mainly detected in HBV-infected patients from central Europe. Coinfection of HBV and HDV has been detected in some HBV-infected people in different parts of the world. Some studies have shown that coinfection of HDV in HBV-infected patient exhibit severe liver diseases and are prone to develop complications such as liver cirrhosis. Diagnosis of coinfection of HBV/HDV is important in some regions of the world. Also, management of coinfection should be well understood by physicians. A comprehensive description of coinfection of HBV/HDV has been provided in this chapter.