Inhaled corticosteroids have now become established as first-line therapy for patients with persistent asthma. Corticosteroids are the only currently available asthma therapy that suppress inflammation in asthmatic airways, and they inhibit almost every aspect of the inflammatory process in asthma. Inhaled corticosteroids are effective in most patients with asthma, irrespective of age or asthma severity. They not only control asthma symptoms and improve lung function but also prevent exacerbations and may reduce asthma mortality and the irreversible changes in airway function that occur in some patients. The dose-response curve to inhaled corticosteroids is relatively flat, and there is increasing evidence that addition of another class of therapy (long-acting inhaled β2-agonists, low-dose theophylline, or antileukotrienes) may be preferable to increasing the dose of inhaled corticosteroids in patients with moderate-to-severe asthma. Inhaled corticosteroids are convenient to use and are the most cost-effective treatment currently available for long-term asthma control. A small proportion of patients are resistant to the antiinflammatory effects of corticosteroids. Future developments may include inhaled corticosteroids with even fewer systemic effects or more specific antiinflammatory drugs.