Allergic Bronchopulmonary Aspergillosis (ABPA) is a severe respiratory disease caused by the fungus Aspergillus fumigatus (Af). It occurs as secondary complication mostly in patients with atopy and cystic fibrosis. The standardized and well-characterized allergens are essential for the immunodiagnosis of ABPA as well as for understanding the pathophysiology of the disease. Molecular cloning was resorted to obtain purified Af allergens for such studies. Currently, twenty-two recombinant Af allergens have been identified and characterized and several of these can be used as standardized allergens in in vitro and in vivo diagnosis of ABPA. The knowledge of primary, secondary, and tertiary structures of these allergens may facilitate the identification of immunodominant T and B cell epitopes and may be used to unravel the structure function relationship of these allergens. Such findings may open up novel avenues in the immune modulatory therapy and other effective intervention of the disease.