The frequency of allergic diseases has increased in recent decades. Asthma is one of the most prevalent conditions and a leading cause of morbidity. It affects 3-4% of the population in our geographical setting and extrinsic allergens are detected as the disease's etiological agent in around half of these cases. IgE is one of the molecules involved in the allergic process. Most of the time and resources at asthma units are devoted to corticosteroid-dependent patients. International guidelines for asthma treatment recommend a stepwise therapeutic approach; in the last step, the use of oral corticosteroids is advised when control is not achieved with long-acting beta-2-agonists and high doses of inhaled corticosteroids. No alternatives or complements to oral corticosteroids had been proposed until November 2006, when the latest GINA update included the IgE blocker omalizumab in the last step of asthma treatment. In this paper we discuss the pathogenesis of the allergic reaction and the key importance of IgE in this process in order to highlight the beneficial effects of a drug able to block the circulation of the free form of this immunoglobulin. We also review the most important studies and patents for the efficacy and effectiveness of the drug in the treatment of adults and pediatric patients with asthma and other diseases.