Owing to its major and better recognised burden from both individual and societal perspectives, chronic obstructive pulmonary disease (COPD) is an area of intensive epidemiological, fundamental and clinical research, leading to the publication of more than 10,000 papers each year in the PubMed database. Among these, many report important advances in the understanding of and care for COPD. Epidemiological aspects are the topic of another manuscript in this issue of the European Respiratory Review [1], while the treatment of COPD and its exacerbations will be addressed in other reviews in upcoming issues. Thus, the present paper will focus on more fundamental aspects of pathophysiology, resting and exercise lung mechanics, respiratory muscles and gas exchange, together with more clinical topics, including respiratory symptoms and comorbidities. The purpose of the authors is clearly not to be exhaustive but to focus on points that are likely to have some impact on clinical practice in the relatively short term.

PATHOPHYSIOLOGY Cigarette smoking is the leading cause of COPD in Western countries. Cigarette-associated noxious agents injure the airway epithelium and drive the key processes that lead to specific airway inflammation and structural changes [2]. Once these agents are removed, repair processes should, ideally, bring the airways back to their normal structure and function. In general, an inadequate repair process is thought to play a key role in the development of chronic airflow obstruction in some, but not all, smokers. Indeed, in many subjects most of the inflammatory changes continue despite smoking cessation [3]. This failure of bronchial inflammation to resolve might contribute to systemic changes and ongoing bronchial and lung matrix degradation. In addition to persistent airway inflammation, other major phenomena involved in the disease