Abstract Approximately half of all cancer patients are treated with radiation therapy. However, some tumor cells can escape the lethal effects of irradiation by hypoxia, deregulation of the cell cycle or apoptosis or by increasing their ability to repair the DNA damage induced, resulting in recurrence of disease. In order to overcome these resistance mechanisms, various strategies have been developed. Over the last decade, extensive progress in human genomics and genetic tools has been made. Several methods using DNA or RNA molecules have been developed to target angiogenesis or other cellular functions in order to restore sensitivity to irradiation. In this review, we focus on five classes of nucleic acid-based approaches, (i) gene transfer by recombinant plasmid or virus, (ii) immune-stimulating oligonucleotides, (iii) antisense oligonucleotides, (iv) siRNA and shRNA, and (v) siDNA (signal interfering DNA), which target specific proteins or pathways involved in radioresistance. We review the results of the preclinical studies and clinical trials conducted to date by combining nucleic acid-based molecular therapy and radiotherapy.