The Asthma Control Questionnaire (ACQ) was developed to measure the primary goals of asthma management as identified by international guidelines. All guidelines indicate that to achieve good control, treatment should minimise day- and night-time symptoms, activity limitation, airway narrowing and rescue bronchodilator use and thus reduce the risk of life-threatening exacerbations and long-term morbidity. Three independent studies have provided evidence that the ACQ is valid for measuring asthma control and has strong measurement properties for use both in clinical practice and research. In addition, the smallest change in score that can be considered clinically important has been determined.