In cancer treatment, radiation therapy is second only to surgery in terms of its curative potential. However, radiation-induced tumor cell death is limited by a number of factors, including the adverse response of the tumor microenvironment to radiation treatment and tumor-acquired mechanisms of evasive resistance. Recent attempts to enhance the therapeutic efficiency of ionizing radiation have produced promising results. In this review article, we discuss the development of novel therapeutic strategies for tumor sensitization to radiation therapy. These innovative approaches incorporate the involvement of the immune response and the role of cancer stem cells, as well as direct targeting of signal transduction pathways. Taken together, these concerted efforts demonstrate that the augmentation of radiotherapeutic efficacy results in significantly improved control not only of local disease, but also of metastatic spread and improved overall patient survival.