Intraoperative radiation therapy (IORT) is the delivery of irradiation at the time of an operation. This is performed by different techniques including intraoperative electron beam techniques and high-dose rate brachytherapy. IORT is usually given in combination with external-beam radiation therapy with or without chemotherapy and surgical resection. IORT excludes part or all dose-limiting sensitive structures, thereby increasing the effective dose to the tumor bed (and therefore local control) without significantly increasing normal tissue morbidity. Despite best contemporary therapy, high rates of local failure occur in patients with locally advanced or recurrent rectal cancer, retroperitoneal sarcoma, select gynecologic cancers, and other malignancies. The addition of IORT to conventional treatment methods has improved local control as well as survival in many disease sites in both the primary and locally recurrent disease settings. More recently, there has been interest in the use of IORT as a technique of partial breast irradiation for women with early breast cancer. Given newer and lower cost treatment devices, the use of IORT in clinical practice will likely grow, with increasing integration into the treatment of nonconventional malignancies. Optimally, phase III randomized trials will be carried out to prove its efficacy in these disease sites.