Clinical practice guidelines for radiation therapy in the treatment of lung cancer were prepared by an expert multidisciplinary Panel. This project was supported by a Grant-in-Aid from the Ministry of Health, Labour and Welfare of Japan, with the primary objective to develop efficient practice guidelines for the treatment of lung cancer by systematic review of currently available evidence. We reviewed pertinent evidence from the published literature with a computerized search on MEDLINE, and filled in abstract forms for the most relevant. All abstract forms were reviewed by other experts in the panel. The extracted problems were as follows: the basics for radiotherapy including machines, planning equipments and quality assurance, definitive radiotherapy for medically inoperable or unresectable non-small cell lung cancer, chemoradiotherapy for non-small or small cell lung cancer, prophylactic cranial irradiation, and palliative irradiation for bone and brain metastases. Values for levels of evidence and grades of recommendation for each problem were discussed and approved by the panel. Essentially, the guidelines propose the minimum requirements for clinical practice. These guidelines, therefore, are expected to be useful for individualized treatments for lung cancer patients.