Asthma is an inflammatory disease of the airways even in its clinically mildest manifestation. The pathogenesis is based on complex interactions between inflammatory cells, soluble signal molecules (mediators) and structural cells as well as extracellular components of the airways. Bronchial inflammation is closely associated with bronchial hyperreactivity, airways obstruction and asthmatic symptoms. Airways inflammation causes airflow limitation via (1) acute muscular bronchoconstriction, (2) formation of mucous plugs, (3) thickening of the airway wall, and (4) fibrotic remodelling of the airways ("Remodelling"). The insights into bronchial inflammation as the basis of asthma is of principle significance for the diagnosis, prevention, and treatment of the condition.