This EASL Monothematic Conference is devoted to the study of hepatitis D virus (HDV) and to delta hepatitis, the clinical consequence of infection with HDV and hepatitis B virus (HBV). HDV is unique in several aspects. For the clinican, it is unique in the sense that HDV alone does not cause disease but needs the helper function of HBV. However, dual HBV-HDV infection represents the most severe form of viral hepatitis and development of hepatocellular carcinoma occurs more frequently in patients with chronic delta hepatitis compared to patients with chronic hepatitis B or C. Despite this, little progress has been observed on the management of this devastating disease in the last dceades. This conference on delta hepatitis will provide both for virologists and hepatologists with special interest in viral hepatitis, the opportunity to discuss latest developments and needs on the virology of HDV as well as on the epidemiology, pathogenesis, diagnosis, management and future research needs in delta hepatitis disease.