Aspergillus is a saprophytic mold and its natural habitat is the soil. It is found worldwide indoors and outdoors in potted soil, compost, freshly cut grasses, decaying vegetation and in sewers. Aspergillus produces a bountiful number of spores and releases 2-3 micron sized spores into the air daily. It grows best at 37-40 °C, which is similar to the temperature in the lungs. These spores will remain airborne for a long period of time. It is estimated that humans inhale hundreds of spores daily. Several fungi other than aspergillus have been known to be implicated. Hence, the term allergic bronchopulmonary mycoses would be more appropriate unless the specific fungus is identified - which could be candida, helminthosporium, curvularia, bipolaris, cladosporium, or others. The review article is focused on the prototype allergic bronchopulmonary aspergillosis, its epidemiology, pathogenesis, diagnosis and treatment. Bronchopulmonary aspergillosis should be considered in patients with poorly controlled asthma despite appropriate routine therapy and environmental control. The need for frequent courses of corticosteroids with temporary improvement should raise the index of suspicion and appropriate evaluation be done. Early recognition and prompt initiation of appropriate corticosteroid treatment regimen would reduce the risk of development or progression of bronchiectasis and lung tissue damage. Regular follow up and monitoring serum total IgE level can predict exacerbations and should prompt corticosteroid treatment. Long term follow-up is important as relapses can occur years of remission.