Averill Liebow published a paper in 1975 about definition and classification of interstitial pneumonias in human pathology. His classification was based on histological morphology in different types of idiopathic interstitial pneumonias. Usual interstitial pneumonia (UIP) and desquamative interstitial pneumonia (DIP) have persisted as important histologic groups. However others of his classification as bronchiolitis obliterans with classical interstitial pneumonia (BIP) and giant cell interstitial pneumonia (GIP) have disappeared from subsequent classification. Liebow emphasized that it was histological patterns rather than distinctive diagnostic entities, that could occur in a variety of clinical contexts. Regardless of the clinical context, however, he maintained that precise histological classification of interstitial pneumonias provides clues to etiology, pathogenesis, natural history, and prognosis. In other words, although individual histological variations do not offer distinguished diagnostic entities, However each significantly limits the differential diagnosis and can predict treatment response and outcome.