After several nucleoside analogues have been tested against chronic hepatitis B virus (HBV) infection with minimal success, lamivudine seems to be a highly effective new therapeutic option. This review focusses on nucleoside metabolism and on the molecular action of lamivudine as well as on results of clinical studies for several indications. We report on results of trials on the use of lamivudine for chronic HBV infection, chronic HBV under immunosuppression and prophylaxis or treatment of HBV reinfection before or after orthotopic liver transplantation. Aspects of combination therapy of different nucleoside analogues as well as on combination of lamivudine with interferon are also highlighted. Although lamivudine seems to be highly effective in most patients at the start of therapy, development of resistance by mutations in the viral polymerase is a significant clinical problem. The mode of resistance development is compared with the situation in HIV infection. Possible cross-resistance with other nucleoside analogues and the perspectives of lamivudine therapy are also considered.