A number of oncolytic viruses (OVs) have undergone extensive preclinical and preliminary clinical evaluation. In addition to their intrinsic antitumor activities, OVs have the potential to enhance the radiation response in a range of tumor types. In this review, significant advances in OV therapy are discussed, with a specific emphasis on those strategies that are likely to be of clinical use. In particular the use of wild-type OVs (eg, reovirus and measles) and engineered unarmed OVs (eg, adenoviruses and HSVs) as radiosensitizers, and engineered armed OVs that express genes that can enhance the radiation response are highlighted. This latter group includes strategies such as virus-directed enzyme prodrug therapy, radiosensitizing cytokine therapy (eg, TNFalpha) and radionuclide uptake (eg, the sodium iodide symporter and the norepinephrine transporter) gene therapy. Future directions for the clinical development of OVs are also discussed.