Two-thirds of exacerbations are associated with respiratory tract infections or air pollution, but one-third present without an identifiable cause.17 Exacerbations remain poorly understood in terms of not only cause but also treatment and prevention. Although the management of an acute exacerbation has been the primary focus of clinical trials, the prevention of acute exacerbations has not been a major focus until recently. Most current COPD guidelines focus on the general diagnosis and evaluation of the patient with COPD, the management of stable disease, and the diagnosis and management of acute exacerbations.1,20 Although current COPD guidelines state that prevention of exacerbations is possible, little guidance is provided to the clinician regarding current available therapies for the prevention of COPD exacerbations.1,20 Moreover, new therapies have promise in preventing acute exacerbations of COPD (AECOPD) and would benefit from critical review of their efficacy in the exacerbation prevention management.21-23 The American College of Chest Physicians (CHEST) and Canadian Thoracic Society (CTS) jointly commissioned this evidence-based guideline on the prevention of COPD exacerbations to fill this important void in COPD management.