Bronchiectasis is a condition of increasing incidence and prevalence around the world. Many different diseases have been associated with bronchiectasis, and their treatment can differ widely. Recent guidelines have helped to approach aetiological diagnosis but it is still a complex process. Identifying the cause of the bronchiectasis may determine a change in the treatment of a large group of subjects. That is one of the main reasons why the aetiological diagnosis is crucial in the proper management of bronchiectasis patients. Postinfectious bronchiectasis is the most frequent entity among different studies, but a high percentage of cases still remain without a clear aetiology. Bronchiectasis related to allergic bronchopulmonary aspergillosis (ABPA), immunodeficiencies with antibody production deficiency, primary ciliary dyskinesia, cystic fibrosis and alpha-1-antitrypsin deficiency, among others, require a specific management that may improve quality of life and prognosis in a large group of individuals. Therefore, the aim of this article is to review the main bronchiectasis related diseases and to simplify the aetiological diagnosis, in order to improve the management of bronchiectasis patients, especially in those where a specific treatment is available.