Radiation plays an important role in the management of patients with non-small-cell carcinoma of the lung. Understanding the impact of radiation on this tumor and on normal tissues requires a knowledge of the natural history of the tumor, and of basic sciences, including radiation physics and biology. This review gives a brief outline of the scientific basis of radiotherapy, followed by a discussion of some practical issues concerning radiation tolerances of tissues within the thorax, the acute and late sequelae of radiation, and the treatment planning process. The role of radiotherapy is explored in the following settings: Radical radiation with curative intent for early stage disease, adjuvant mediastinal irradiation for completely resected tumors, radiation of known residual disease after surgical resection, preoperative radiation, prophylactic cranial radiation, radiation of locally advanced unresectable disease, and, finally, radiation with palliative intent in patients with metastatic disease. Pertinent studies, with the emphasis on randomized trials, are outlined to document the present state of understanding with respect to the impact of radiation in each of these situations. Several of the controversies in this area are addressed, with particular emphasis on selection of patients for high-dose radiation and recent results of combined modality treatment with radiation and chemotherapy.