Every chapter in the GOLD 2017 Report has been revised, with new figures and tables provided, and the references extensively updated. The definition of COPD is still problematic and is essentially a description, but it has been simplified to: “COPD is a common, preventable and treatable disease that is characterized by persistent respiratory symptoms and airflow limitation that is due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles or gases.” This definition now specifically includes persistent symptoms. In current cigarette smokers, symptoms measured by the COPD Assessment Test (CAT), exacerbations and increased airway thickening on computerized tomograph, may occur without airflow limitation as measured by FEV1/FVC ratio. These individuals do not meet the normal criteria for COPD because they do not have spirometric airway obstruction; however, it is very likely that they may have obstruction of small airways and represent an earlier stage of the disease, and they may need treatment. Indeed, a recent longitudinal study found that smokers with mucus hypersecretion (chronic bronchitis) are at risk of developing airway obstruction (COPD). This finding highlights the need to study early disease, the inadequacy of spirometry in defining the diagnosis, and the need for better tests of small airway obstruction and air trapping.