Idiopathic interstitial pneumonia (IIP), or noninfectious pneumonia[1] 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.

[2] Classification can be complex,[3] and the combined efforts of clinicians, radiologists, and pathologists can help in the generation of a more specific diagnosis.

[4][5] Idiopathic interstitial pneumonia can be subclassified based on histologic appearance into the following patterns:[6][7] Usual interstitial pneumonia is the most common type.