Idiopathic interstitial pneumonia (IIP), or noninfectious pneumonia are a class of diffuse lung diseases. These diseases typically affect the pulmonary interstitium, although some also have a component affecting the airways (for instance, cryptogenic organizing pneumonitis). There are seven recognized distinct subtypes of IIP. Idiopathic interstitial pneumonia (IIP), or noninfectious pneumonia are a class of diffuse lung diseases. These diseases typically affect the pulmonary interstitium, although some also have a component affecting the airways (for instance, cryptogenic organizing pneumonitis). There are seven recognized distinct subtypes of IIP. Classification can be complex, and the combined efforts of clinicians, radiologists, and pathologists can help in the generation of a more specific diagnosis. Idiopathic interstitial pneumonia can be subclassified based on histologic appearance into the following patterns: Usual interstitial pneumonia is the most common type.