High energy X-rays have been used for cancer therapy since their discovery in 1895. Major radiobiological discoveries and technological advances in radiation physics have greatly increased the accuracy of radiation. The recent integration of radiation therapy and imaging systems provides radiation oncologists with sophisticated dose delivery capability allowing continued improvements in the control of loco-regional and metastatic disease while decreasing toxicity. Key technical aspects of current radiation therapy are described with examples extending to several clinical areas. J. Surg. Oncol. 2011;103:627–638. © 2011 Wiley-Liss, Inc.