During the last years much attention has been given to the investigation of the roles of specific growth modulators acting on liver cell populations. HGF functions as a pleotropic factor in the liver as well as in other extrahepatic tissues. The hepatic stem cell compartment is thought to play a major role in liver tissue restoration. Mechanisms of cell growth and cell death of the liver are described in detail, with particular emphasis on apoptosis. The functions of HBV-pX protein and the roles of hepatitis B virus gene expression relation to hepatocellular carcinoma are discussed. Techniques for obtaining human and nonhuman hepatocytes and other liver cell types and for efficient transfer and expression of genes in hepatocytes and liver-derived cell lines are presented.