Radiation plays an important role in the multimodal management of tumors of the gastrointestinal (GI) system. Intensity-modulated radiation therapy (IMRT) is a technological development that was introduced to limit the acute and late toxicities commonly associated with conventional radiation therapy. Numerous preclinical dosimetric comparisons of conventional and intensity-modulated radiation plans for treating various GI tumors have been reported. In general, these studies have shown that IMRT can spare organs at risk in the high-dose region while maintaining adequate target coverage. Clinical reports on the efficacy and tolerability of IMRT are emerging. This review provides a description of the differences between conventional irradiation and IMRT and discusses the preclinical and early clinical investigations of the role of IMRT in the treatment of GI tumors. The ultimate role of IMRT in GI tumor management will be determined through further clinical study.