Nicola A. Hanania, MD, MS, FRCPC, Editor

Louis-Philippe Boulet, MD, FRCPC, Editor

Asthma and chronic obstructive pulmonary disease (COPD) are common airway diseases that often have overlapping clinical presentation, which may cause a major challenge for the health care providers. This overlap, although recognized for many years, has been called Asthma COPD Overlap (ACO). There is no consensus on the exact definition of ACO, although several epidemiologic studies suggest that its presence is associated with worse clinical outcomes than asthma or COPD. In the following series, our invited authors detail the various features associated with ACO, focusing on current knowledge and outlining future needs. The various articles discuss the definition, pathophysiology, and epidemiology of this entity. Other articles of this series deal with the development of early signs of COPD in asthmatic subjects, as well as the genetic determinants in addition to physiological changes and imaging features observed in patients with ACO. As most ACO patients have a significant history of smoking, the role of smoking in airway/lung changes is discussed. In other articles, the authors discuss the use of biomarkers and phenotyping of ACO subsets and provide an overview of pharmacologic and nonpharmacologic treatments of ACO. In addition, the potential new therapeutic targets and unmet needs to improve management of this condition are discussed.