Integrative cardiopulmonary exercise testing has evolved from a specialized research laboratory tool into a valuable clinical test that is especially useful for assessment of symptoms of exertional dyspnea and exercise intolerance. There is increasingly convincing evidence that evaluation and quantitation of impairment are enhanced by use of exercise testing. In particular, exercise testing has the advantages of objective determination of abnormal exercise tolerance, increased sensitivity for subtle pulmonary gas exchange abnormalities, the ability in many instances to identify unsuspected or unanticipated non-pulmonary causes of impairment, and a useful quantitation of impairment. Although exercise testing is especially valuable in those with mild-to-moderate lung disease in whom questions about the presence of occupational disease and its contribution to impairment are raised, other important questions can be addressed with these methods (Table 10). Therefore there is a high likelihood that the logic of assessing work capacity while the subject performs work will become increasingly clear.