Current oncolytic virotherapy strategies are based in the accumulated understanding of the common molecular mechanisms displayed during cell transformation and viral infection, like cell cycle and apoptosis deregulations. Oncolytic virotherapy aims to achieve a strong cytolytic effect, highly restricted to transformed cells. Here, we describe the oncolytic virotherapy defined as the use of viruses like antitumor agents (wild and gene-modified oncolytic viruses) and the developed strategies to increase antitumor efficacy and safety. In addition, we discuss the advances and challenges concerning the use virotherapy in animal models and clinical trials. Some clinical trials of virotherapy have demonstrated promising results, particularly when combined with standard antineoplastic therapies. These preliminary accomplishments are opening the field for more research in several aspects, like vector modifications, pharmacodynamics, biosafety, new clinical applications, etc.