Chapter opening: Asthma is a disease characterized by (1) reversible airway obstruction; (2) airway inflammation; and (3) increased airway responsiveness to a variety of stimuli (hyperreactive airways). It is estimated that 10 million persons in the United States have asthma and that 5–10% of children suffer from this disease. The prevalence of asthma may be even greater if children with mild symptoms such as chronic cough, recurrent croup, and exercise-induced asthma (EIA) are included.