A number of chronic respiratory diseases including chronic bronchitis, asthma, cystic fibrosis and bronchiectasis are characterized by mucus hypersecretion. Following damage to the airway epithelium, a repair process of dedifferentiation, regenerative proliferation and redifferentiation takes place that is invariably accompanied by mucus hypersecretion as a key element in the host defence mechanism. In chronic respiratory diseases, however, excessive mucus production leads to a pathological state with increased risk of infection, hospitalization and morbidity. An understanding of the mechanisms that underlie and maintain this hypersecretory phenotype is therefore crucial for the development of rational approaches to therapy. Despite a high and increasing prevalence and cost to healthcare services and society, mucus hypersecretion in chronic respiratory disease has received little attention until recently, probably because of the difficulties inherent in studying this pathology. Only in the last few years have some of the genes involved in mucus secretion been characterized. The recent availability of genomic sequence information and specific antibodies has led to an explosion of interest in this area making this publication particularly timely. This book draws together contributions from an international and interdisciplinary group of experts, whose work is focused on both basic and clinical aspects of the problem. Coverage includes epidemiology, airways infection and mucus hypersecretion, the genetics and regulation of mucus production, models of mucus hypersecretion, and the implications of new knowledge for the development of novel therapies.