The book covers both the molecular aspects of hepatitis B virus replication and gene expression in vivo and in model systems, and the clinical impact of genetic variants or immunological response in chronic infection. Major emphasis is laid on the molecular mechanisms underlying hepatitis B virus-associated liver carcinogenesis and their possible relevance to therapy and to the prevention of infection. Rational approaches to design novel vaccines or cytokine treatments, as well as strategies to develop vectors for liver-directed gene therapy, are discussed.