Airway inflammation plays a central role in the pathogenesis of asthma and COPD and represents the underlying process of patients' symptoms and exacerbations. The topics covered include Exhaled Nitric Oxide, Induced Sputum, and Exhaled Breath Condensate, the three modalities that have been studied most extensively, in an attempt to provide information about Technical Considerations and ''Normal'' Values of candidate biomarkers, as well as insights on Application in Clinical Practice in Asthma and COPD.