Chronic obstructive pulmonary disease (COPD) continues to be an important cause of morbidity, mortality, and health-care costs worldwide. It is a global health issue, with cigarette smoking being an important risk factor universally; other factors, such as exposure to indoor and outdoor air pollution, occupational hazards, and infections, are also important. As the global population ages, the burden of COPD will increase in years to come. Prevalence estimates of the disorder show considerable variability across populations, suggesting that risk factors can affect populations differently. Other advances in our understanding of COPD are increased recognition of the importance of comorbid disease, identification of different COPD phenotypes, and understanding how factors other than lung function affect outcome in our patients. The challenge we will all face in the next few years will be implementation of cost-effective prevention and management strategies to stem the tide of this disease and its cost.

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality in countries of high, middle, and low income. Estimates from WHO's Global Burden of Disease and Risk Factors project1 show that in 2001, COPD was the fifth leading cause of death in high-income countries, accounting for 3·8% of total deaths, and it was the sixth leading cause of death in nations of low and middle income, accounting for 4·9% of total deaths. In this same report, COPD was also estimated to be the seventh and tenth leading cause of disability-adjusted life years in countries of high income and in those of low or middle income, respectively.1 COPD has been the focus of recent Reviews in The Lancet, including one from 2003 by Calverley and Walker2 and another published in 2004 by Pauwels and Rabe.3 Our Review will focus on advances in understanding of COPD and its risk factors, prevalence, and natural history since these Reviews were published, address some of the questions that still persist, and raise some of the issues that health-care planners will have to consider as the burden of COPD increases as the world's population ages.