Dyspnea, described as breathlessness or shortness of breath, is usually caused by cardiopulmonary disease. The role of imaging in chronic dyspnea (>1 mo in duration) with suspected pulmonary origin is reviewed as suggested by the American College of Radiology Appropriateness Criteria Expert Panel on Thoracic Imaging. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.