Purpose: To provide guidance to physicians and patients with regard to the use of adjuvant external beam radiation therapy (RT) in locally advanced non-small cell lung cancer (LA NSCLC) based on available medical evidence complemented by consensus-based expert opinion. Methods and materials: A panel authorized by the American Society for Radiation Oncology (ASTRO) Board of Directors and Guidelines Subcommittee conducted 2 systematic reviews on the following topics: (1) indications for postoperative adjuvant RT and (2) indications for preoperative neoadjuvant RT. Practice guideline recommendations were approved using an a priori-defined consensus-building methodology supported by ASTRO and approved tools for the grading of evidence quality and the strength of guideline recommendations. Results: For patients who have undergone surgical resection, high-level evidence suggests that use of postoperative RT does not influence survival, but optimizes local control for patients with N2 involvement, and its use in the setting of positive margins or gross primary/nodal residual disease is recommended. No high-level evidence exists for the routine use of preoperative induction chemoradiation therapy; however, modern surgical series and a post-hoc Intergroup 0139 clinical trial analysis suggest that a survival benefit may exist if patients are properly selected and surgical techniques/postoperative care is optimized. Conclusions: A consensus and evidence-based clinical practice guideline for the adjuvant radiotherapeutic management of LA NSCLC has been created addressing 2 important questions.