Among the possibilities for hemophilia B gene therapy, the following approaches can be distinguished: (1) correction of a defective gene copy using in vivo or ex vivo genome-editing tools, (2) control of protein translation without affecting the gene sequence using RNA interference, and (3) delivery of a functional gene copy of the F9 gene with the help of viral vectors in vivo or ex vivo in autologous cells of the patient, with subsequent transplantation. The gene discussed is F9; the disease is hemophilia B.