TOPDOCS is a prospective cohort study including COPD patients from currently six study centers in Switzerland. Patients with COPD GOLD stages I-IV will be enrolled and followed-up annually for at least 3 years. Yearly assessments will include a detailed patient history, quality of life and activity questionnaires, history of exacerbations, lung function, measurements of exercise capacity, measurements of vascular function, exhaled breath analysis and blood sampling. The overall objective of the project is to establish a meticulously characterized cohort of COPD patients living in Switzerland in order to allow high quality research on the pathogenesis, treatment and complications of COPD. The specific aim of the project is to determine clinically relevant COPD phenotypes and biological factors influencing vascular function in COPD patients.