Oncolytic viruses (OVs) are an emerging treatment option for multiple cancer types and have recently been the focus of extensive research to develop their therapeutic potential. OVs have been put into the improvement of their efficacy and safety profiles. There are many viruses which either have naturally oncolytic properties or have been engineered to specifically lyse tumor cells. The great feature of this therapy is that these viruses are able to specifically target tumor cells and thus healthy tissue is not damaged during the course of the treatment. There are multiple ways to improve the specificity of OVs, for example, taking advantage of pathways that are upregulated in tumor cells and not healthy cells and engineering a virus which relies on such a pathway for successful infection thereby rendering the virus incapable of infecting healthy tissue.