The basic principles of gene therapy, ex vivo and in vivo gene transfers and various vectors have been reviewed first in the paper. Then the models for clinical application are shown, including the recent results of experimental studies, with special regard to the treatment of liver diseases and amongst them hepatocellular carcinoma. Gene therapy is still in preclinical stage. Due to the ongoing intensive genetic studies and if the existing problems being resolved in this field, we can predict that the early years of this millennium gene therapy will be a useful modality in the clinical hepatology as well.