Abstract Bronchiectasis is defined as irreversible, abnormal dilatation of one or more bronchi, with chronic airway inflammation, associated chronic cough and sputum production, recurrent chest infections and airflow obstruction. The diagnosis of bronchiectasis is made clinically and confirmed by high-resolution computed tomography (HRCT) of the chest. Patients with a diagnosis of bronchiectasis should be referred to a specialist unit for investigation and management. This article deals with non-cystic fibrosis (CF) bronchiectasis. Bronchiectasis is a common structural endpoint that can be reached by several pathological routes from foreign body obstruction to post-infectious damage (tuberculosis), genetic defects (cystic fibrosis), abnormal host defence (ciliary dyskinesia and hypogammaglobulinaemia) and autoimmune disease (rheumatoid arthritis and ulcerative colitis). About half of all cases are called idiopathic since no known underlying cause is identified following detailed investigation. These patients typically have bilateral, predominantly lower lobe disease, and chronic rhinosinusitis. The underlying pathogenesis of bronchiectasis is not known. Innate and adaptive immune mechanisms have been implicated. There appear to be two stages to the disease process: an initial insult followed by a continuing inflammatory process encompassing recurrent infection and progressive lung damage. Abnormalities in immune regulation may predispose to bronchiectasis, both at the time of the initial insult that sets off the disease and during the on-going inflammatory process that ends in progressive lung damage. Immunogenetic evidence suggests a link between the extent of natural killer (NK) cell activation and disease susceptibility. Further evidence for adaptive immune mechanisms includes a genetic association with HLA-DR1, DQ5 and increased susceptibility to idiopathic bronchiectasis.