The integrity of the airway epithelium in asthma patients is often disrupted, with loss of epithelial cell-cell contacts. Airway epithelial barrier dysfunction may have important implications for asthma, since structural epithelial barrier function is tightly interwoven with the ability of the epithelium to regulate the immune system. We propose that changes at the airway epithelial barrier play a central role in the sensitization to allergens and pathogenesis of allergic asthma. Many of the recently identified susceptibility genes for asthma are expressed in airway epithelium. However, the exact mechanisms by which the expression of epithelial susceptibility genes translate into a functionally altered response to aeroallergens in asthma is still unknown. In this review we will focus on the role of airway epithelial barrier function in the susceptibility to develop allergic asthma, and discuss therapeutic strategies aimed at the epithelial barrier. This article is protected by copyright. All rights reserved.