Chronic airway inflammation is a general feature of some types of asthma, cystic fibrosis (CF), bronchopulmonary dysplasia (BPD), and chronic obstructive pulmonary disease (COPD). This chronic inflammation is associated with structural changes in the airway wall and parenchyma, which affect the functional properties of these tissues. It is these changes that are defined as remodeling. However, association between inflammation and remodeling cannot be regarded as proof of causality. These airway changes should not be considered as fixed; there is a dynamic state of cell and matrix protein turnover in both diseased and healthy airways. Knowledge of the type and distribution of morphological changes that can (ir) reversibly impair lung function may potentially lead to the development of more effective treatment. Unfortunately, virtually all our knowledge comes from studies of the mature airway. We do not know whether in children the response of cells to inflammatory stimuli is greater or less than in adults, or the capacity of the developing airway to restore itself to normality.