Inclusion Criteria:  20 of the 600 will be healthy controls: ages 30-55 years; with no smoking history (< 100 cigarettes in lifetime), including vaping and cannabis use; post-bronchodilator forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) > 0.70; post-bronchodilator FEV1 > 80% predicted; post-bronchodilator FVC > 80% predicted; Chronic Airway Assessment Test (CAAT) score < 10; and willingness to also participate in the bronchoscopy sub-study. Approximately one-third of the 580 will be GOLD 0 participants: ages 30-55 years; with ≥ 10 pack-year smoking history; post-bronchodilator FEV1/FVC > 0.70 and FEV1 > 80% predicted; and Chronic Airway Assessment Test (CAAT) score ≥ 10. This early COPD group has been chosen because it is not currently well-represented in COPDGene and SPIROMICS cohorts. Approximately one-third of the 580 will be Preserved Ratio Impaired Spirometry (PRISm) participants: ages 30-55 years; with ≥ 10 pack-year smoking history; post-bronchodilator FEV1/FVC > 0.70 and FEV1 < 80% predicted. This early COPD group was enrolled in small numbers in the COPDGene study, but was excluded from SPIROMICS. Approximately one-third of the 580 will be GOLD 1-2 participants: ages 30-55 years; with ≥ 10 pack-year smoking history; post-bronchodilator FEV1/FVC < 0.70 and FEV1 50-80% predicted. This early COPD group has been chosen because it is also not currently well-represented in the first funded phase of the COPDGene and SPIROMICS cohorts.  Exclusion Criteria:  Severe asthma, which is defined as any of the following:  Current (i.e., at the time of the visit) Global Initiative for Asthma (GINA) Step 4 or higher therapy (medium dose inhaled corticosteroids (ICS)/long-acting beta agonist (LABA) or high dose ICS or add-on long-acting muscarinic agonist (LAMA); Medium dose > 250 fluticasone propionate, = 100 fluticasone furoate, > 200 beclomethasone, > 400 budesonide, > 220 mometasone). We will accept low-dose ICS/LABA or medium dose ICS; or Three or more unscheduled healthcare visits (provider/urgent care/ER) for asthma in the past 12 months; or One asthma hospitalization in the past 12 months. Concurrent participation in a therapeutic trial where treatment is blinded. Active pregnancy at the time of the baseline visit or planning to become pregnant during the course of the study. This special population is being excluded to minimize potential for fetal radiation exposure. Cognitive dysfunction that prevents the participant from completing study procedures. BMI > 35.0 kg/m^2 at baseline, due to the effects of body weight on CT scan imaging quality. The presence of a respiratory condition other than COPD or asthma, or of a comorbid condition that in the judgment of the investigator may be the principal cause of respiratory symptoms (e.g., dyspnea or decreased exercise tolerance). Any illness expected to cause mortality in the next three years. Any implanted metallic devices or prosthesis above the waist that could degrade thoracic CT scan image quality. History of thoracic radiation or thoracic surgery with resection of lung tissue.