Asthma control may be defined in several ways, but in clinical practice refers to the achievement of an acceptable clinical state, often based on goals of asthma management. It differs from the assessment of disease severity, which quantifies departure from 'normal'. Most references to asthma control in the current literature refer to one or more endpoints rather than a comprehensive composite assessment based on relevant clinical features of the disease. Recent developments have been the introduction of validated measurement tools such as the Asthma Control Questionnaire and Asthma Control Diary, which include symptoms, beta-agonist use and a measure of airway calibre, each scored on a 7-point scale and then aggregated. An alternative view is that a wholly patient-focused outcome (based entirely on patient recall of symptoms over the last week or month) is preferable. In general, however, care-givers appear to favour the inclusion of objective measures, and a range of indicators of disease activity are being investigated, including airway hyperresponsiveness and markers of airway inflammation. The potential value of the wider use of a composite measure of clinical control is being increasingly recognized, and further attempts to develop, validate and apply a simple tool suitable for use in primary care are underway.