Allergen avoidance should be considered as a first line of defense for all types of allergic disease. For some allergens, such as the common pollens, significant avoidance may be difficult or even impossible to accomplish without major alterations in lifestyle. For others, however, particularly the common indoor allergens, avoidance is a very real option that can be achieved through practical environmental control measures. In addition to the inherent logic of allergen avoidance, there are substantial data to support its efficacy in the treatment of patients with atopic disease, particularly asthma. Further, there is an emerging body of evidence to support its role in the prevention of allergic disease in infants and children. In this article, recent research advances in the areas of indoor allergens, environmental control, and allergen avoidance are reviewed.