The idiopathic interstitial pneumonias are a group of diffuse parenchymal lung diseases that manifest varying patterns of inflammation and fibrosis histopathologically. These disorders are classified most accurately by the combination of histopathology on lung biopsy with clinical and radiographic findings. A pattern-based approach to the histopathology of the lung biopsy, as examined at low magnification, immediately helps narrow the diagnostic possibilities. The technique can be applied by pulmonologists and pathologists in assembling a cogent differential diagnosis. More subtle histopathologic findings in the biopsy (eg, granulomas, necrosis, eosinophils) help narrow this differential. This pattern-based histopathologic technique fosters close interaction between pulmonologists and general pathologists during the evaluation of the patient who has interstitial lung disease and has undergone surgical biopsy.