Lung resection provides the best chance of cure for individuals with early-stage non-small-cell lung cancer. Lung resection will lead to a decrease in lung function. The population that develops lung cancer often has concomitant lung disease and a reduced ability to tolerate further losses in lung function. The goal of the preoperative pulmonary assessment of individuals with resectable lung cancer is to identify those individuals whose short- and long-term morbidity and mortality would be unacceptably high if surgical resection were to occur. Pulmonary function measures such as the forced expiratory volume in 1 second (FEV1) and the diffusing capacity for carbon monoxide (DLCO) are useful predictors of postoperative outcome. When lung function in not normal, the prediction of postoperative lung function from preoperative results, and the assessment of exercise capacity, can help to clarify the risks. Testing algorithms and published guidelines help to direct the order of testing. Interventions that allow us to consider resection outside of the guidelines, or to maximize the potential to tolerate lung resection, help us to offer potentially curative treatment to as many as possible. Knowledge of alternative treatment options will help to guide those deemed unfit for resection.