The connection between asthma and rhinitis is not a new discovery. Significant progress has been made in understanding the relationship of these two conditions, however, and the implications of the asthma–rhinitis link make it increasingly important. Patients who have asthma and rhinitis tend to have more severe disease with higher treatment costs. Treatment of rhinitis may improve asthma control, and early treatment of allergies may prevent the development of asthma. This article more fully explores the epidemiologic, pathophysiologic, and clinical relationships between asthma and rhinitis.