Inclusion Criteria:  Clinical stage I NSCLC (T1 or T2a, N0, M0) by integrated PET/CT scan performed within 90 days of treatment. Biopsy is strongly encouraged. In the event biopsy is not performed, rationale must be provided for performing empiric treatment. Patients with hilar or mediastinal lymph nodes ≤ 1 cm and no abnormal hilar or mediastinal uptake on PET will be considered N0. Mediastinal lymph node sampling by any technique is allowed but not required. Patients with > 1 cm hilar or mediastinal lymph nodes on CT or abnormal PET (including suspicious but nondiagnostic uptake) may still be eligible if directed tissue biopsies of all abnormally identified areas are negative for cancer. First primary NSCLC on the ipsilateral side. At least 18 years of age.  Clinically eligible for either treatment (surgical resection or SBRT). Because this is a pragmatic study and treatment decisions are at the discretion of the treating physicians and their patients, patients must be eligible for either treatment. In order to be considered eligible for either treatment, patients must have:  ECOG performance status ≤ 2 No home oxygen use FEV1 and DLCO ≥ 40% predicted No symptomatic congestive heart failure as documented by NYHA I-II functional classification Been deemed operable by a thoracic surgeon, per clinical visit or review of the medical record and as documented by e-mail, tumor board, study meetings, or other acceptable source documentation. In addition to operability, the surgeon must define what anticipated surgical approach and procedure would be undertaken. Been deemed treatable by a radiation oncologist with 5 or fewer fractions of SBRT, per clinical visit or review of the medical record and as documented by e-mail, tumor board, study meetings, or other acceptable source documentation. In addition to suitability for SBRT, the radiation oncologist must define which dose and fractionation would be undertaken. Ability to understand and willingness to sign an IRB-approved written informed consent document.  Exclusion Criteria:  A history of other invasive malignancy with the exception of malignancies for which all treatment was completed at least 3 years before registration and the patient has no evidence of active disease. Suspicious or biopsy proven low-grade neuroendocrine carcinoma (carcinoid). Received prior intra-thoracic radiation therapy that would overlap with the current lung cancer. Previous chemotherapy, radiotherapy, or surgical resection specifically for the lung cancer being treated. Prior lung resection on the ipsilateral side. Patients with central tumors requiring a sleeve lobectomy or pneumonectomy. "Ultra-central" lesions (defined as a lesion that directly contacts or overlaps the trachea, main bronchus, esophagus, or pulmonary vessels), or those for which a more extended fractionation would be required to safely treat with SBRT. Concurrent enrollment in a therapeutic trial for the index cancer.