Airway inflammation is a key pathophysiological feature of asthma. The characteristics and mechanisms of inflammation in asthma have been defined in recent years, and now asthma management guidelines recommend the use of antiinflammatory therapy to improve asthma control, reverse exacerbations, and prevent future deterioration (1). These advances in the understanding and treatment of asthma have identified the need to monitor airway inflammation in the day to day management of asthma and also in research. Sputum analysis has emerged as an important marker of airway inflammation in asthma (2). It is reliable, is comparatively noninvasive, and can be obtained on multiple occasions, making it an ideal means to monitor airway inflammation in asthma. This chapter describes the use of sputum analysis in asthma, with a particular focus on how induced sputum analysis has contributed to an understanding of the pathophysiological characteristics of airway inflammation in asthma.