The pronounced variability in the incidence and severity of chronic respiratory diseases such as asthma and COPD, makes effective treatment more difficult, and the social and economic costs of these diseases all the greater. Acute exacerbations are multi-factorial in origin, and are known to be linked with a number of factors including allergens, atmospheric pollution and infectious agents. Effective treatment requires a similarly complex approach that addresses each of the component causes. This text brings together current knowledge of the epidemiology and pathophysiology of these episodes, and the latest experimental models by which researchers are seeking to improve our understanding of their incidence and progression. The authors evaluate the individual efficacy of current treatments in the light of this knowledge and present new recommendations for formulating effective therapeutic regimes.