COPD is a heterogeneous lung condition characterized by progressive loss of lung function causing increasing breathlessness and loss of quality of life. While the predominant mechanism of lung injury in the US is cigarette smoke exposure, the condition is due to an admixture of emphysema and airways disease. This unpredictable mix of tissue pathology is indiscernible by conventional spirometric measures of lung function. This has lead to the recruitment of very large numbers of subjects into clinical studies to include the various subsets of disease. Recently, the NHLBI put forth a consensus statement specifying the need for new techniques to "phenotype" the pulmonary component of COPD, including image-based analysis. Our overall hypothesis is that airway characteristics in subjects with COPD are independent predictors of disease pathophysiology and clinical indices of lung function. Aim 1 of this application is to analyze chest CT scans from 3 independent cohorts and correlate the structural characteristics with clinical and spirometric parameters