One aim of caring for adults and children with asthma should be the identification and treatment of the functional impairments that are troublesome to these patients in their daily lives. Studies have shown that correlations between measures of clinical asthma severity and control and health-related quality of life (HRQL) impairment are only weak to moderate. Therefore, HRQL must be measured directly. In recent years, HRQL questionnaires have been developed and validated to measure the functional (physical, social, emotional, and occupational) impairments that are important to both adults and children with asthma. Most questionnaires are now available in a range of languages. More recently, methods have been developed for the clinical interpretation on HRQL data. Assessment of asthma-specific HRQL can be included in both clinical trials and clinical practice, in conjunction with the conventional measures of airway function, to provide a complete picture of patients' health status.