Gene therapy involves the use of specific genes to treat human diseases and is thus critically dependent on efficient gene delivery systems. Although a variety of systems for such gene delivery are under development, HSV has unique advantages in terms of its large genome size and for gene delivery in the nervous system because of its ability to enter a latent state in neuronal cells. Considerable progress has been made in the effective disablement of this virus whilst retaining its ability to deliver genes and in producing long term expression of the foreign gene. Although much remains to be achieved in the further disablement of the virus and its testing in rodent and primate models of human diseases, it is likely that these viruses may ultimately be of use in human gene therapy procedures particularly for otherwise intractable neurological diseases.