SummaryAfter a short description of the Hepatitis B virus (HBV>, its newly associated antigen-antibody systems are briefly introduced. The natural course of hepatitis is then presented with regard to the evolution of these serological markers, whose clinical significance is discussed. An’mmunercsponse responsible for the destruction°f the HBV infected hepatocytes is proposed and related to the various clinical pictures commonly encountered Virus transmission, epidemiology and prognose of hepatitis B are reviewed and also the Possibilities of prevention, i.e. passive (specific and non-specific gamma globulins) and active immunization.