A variety of engineered nanomaterials (ENMs) have been demonstrated to exacerbate allergen-induced lung disease in rodents or cause allergic lung disease in the absence of any allergen. On the other hand, some studies show that ENMs suppress allergen-induced lung disease. Moreover, there are some apparent conflicting reports of exacerbation versus suppression by the same type of ENM. This chapter serves to overview the literature on ENM-allergen interactions that result in exacerbation or suppression of allergic lung disease in rodents. Potential mechanisms are also discussed, including molecular targets revealed by transgenic mouse studies and the role of the allergen corona in mediating the exacerbation of allergic lung disease by ENMs.