The most widely known method of asthma classification is the severity classification recommended in the National Asthma Education and Prevention Program 1997 guidelines, which also formed the basis of the Global Initiative for Asthma guidelines. This method was developed to direct a hierarchy of asthma therapy based on the patient's severity of disease. However, this severity classification has not been validated and has a number of limitations; in particular, it is challenging for physicians to apply reliably. Moreover, it does not allow asthma control to be assessed after the initiation of treatment, even though symptom control is a key objective of the treatment guidelines. A number of tools have been evaluated to provide longitudinal information on asthma control, and some of these have been validated. Clinically relevant measures of inflammation, such as eosinophilic airway inflammation, may also be helpful in classifying asthma and in guiding the use of antiinflammatory therapy. This may be a particularly useful approach in patients who are asymptomatic but have poor lung function, by permitting physicians to determine whether inflammatory processes are active, thus requiring ICS therapy. In the clinical setting, easy-to-use tools are needed to enable longitudinal assessments of symptom control and (ideally) disease progression.