Radiotherapy is one of the main treatment modalities in lung cancer, contributing to both its cure and palliation. Thoracic irradiation has traditionally been considered the mainstay of treatment in inoperable stage III non-small cell lung cancer. However, despite technical developments and the addition of chemotherapy, the curative potential of radiotherapy in this subset of patients is disappointingly poor. The role of radiotherapy as an adjunct to pulmonary resection (preoperative and postoperative) is questionable, but well-designed and executed phase III studies are lacking. An important application of radiotherapy is palliation of tumor-related symptoms in the chest and in metastatic sites, such as bones and brain. In small cell lung cancer, routine applications of radiotherapy include chest radiotherapy in limited disease and prophylactic cranial irradiation in complete responders to chemotherapy, each increasing survival by about 5%.