Herpes Simplex Virus (HSV) has a number of advantages as a gene delivery vector, particularly for the nervous system. Thus, it naturally establishes asymptomatic latent infections of neuronal cells. Moreover, it is readily grown in culture to high titre and has a large genome so allowing it to be used to deliver multiple or very large genes. Considerable progress has been made in effectively disabling the virus so that it does not damage the cells it infects but can still deliver an inserted gene effectively. In addition, it is now possible to obtain long-term expression of the transgene in the nervous system, using regulatory elements derived from the latency-associated transcript of the virus. As well as its use in the nervous system, the virus has also been used to successfully deliver genes to a variety of other cell types, including peripheral blood mononuclear cells and cardiac myocytes within the intact heart. In particular, its ability to deliver genes effectively to replicating cancer cells and to dendritic cells offers considerable potential for the use of this virus in cancer therapy.