Predicting the tumor response to radiotherapy is one of the major goals of human cancer treatment. Identification of the genes that are differentially expressed between radiosensitive and radioresistant cancers by global gene analysis may provide new insights into the mechanisms underlying clinical radioresistance and improve the efficacy of radiotherapy. In this study, we reviewed the published reports identifying sets of discriminating genes using microarray analysis that can be used for characterization and the prediction of response to radiotherapy in human cancers. These reports indicate that many of the identified genes were associated with DNA-repair, apoptosis, growth factor, signal transduction, cell cycle and cell adhesion. Several genes were found to be predictors of the radiation response with various cancers and certain sets of identified genes were also found to predict the radiation response by using clustering analysis. Global gene expression profiling of responders and non-responders can be useful in predicting responses to radiotherapy and may also provide insights into the development of individualized therapies and novel therapeutic targets.