Advances in radiation oncology have been made on three major fronts: biology, physics, and clinical application. Our biological understanding of how radiation kills cells and how malignant cells avoid damage has identified new targets for therapeutic manipulation. Research in physics has yielded sophisticated methods to direct the deposition of radiation energy in ways that enhance target coverage while minimizing dose to normal structures as much as possible. Intensity-modulated radiation therapy (IMRT) and image-guided radiation therapy represent new paradigms in treatment planning and dose delivery. Clinical management of the cancer patient is multidisciplinary. Increasingly, combinations of radiation and chemotherapy, with or without surgery, are enhancing cure rates, often with preservation of organ function. Taken together, these advances have increased the effectiveness of radiation therapy and promise better treatment results in the future.