BACKGROUND:Obstructive sleep apnea (OSA) and chronic obstructive pulmonary disease (COPD) are common conditions; the co-occurrence of these diseases, called the overlap syndrome (OVS), has been associated with poor health outcomes. PURPOSE:The purpose of this Official American Thoracic Society Research Statement is to describe pathophysiology, epidemiology, outcomes, diagnostic metrics, and treatment of OVS, as well as to identify important gaps in knowledge and make recommendations for future research. METHODS:Clinicians and researchers with expertise in sleep medicine, pulmonary medicine, or both were invited to participate. Topics were divided among the participants according to their interest and expertise. A literature search was conducted; the search was not a formal systematic review. Evidence was considered and supplemented with the panelists' nonsystematic clinical observations. Important knowledge gaps were identified. RESULTS:Recommendations for research to fill existing knowledge gaps were made. The recommendations were formulated by discussion and consensus. CONCLUSIONS:Many important questions about OVS exist. This American Thoracic Society Research Statement highlights the types of research that leading clinicians and researchers believe will have the greatest impact on better understanding the spectrum of disease, improving diagnosis, and optimizing therapy.