The document discusses interstitial lung diseases (ILDs) and diffuse parenchymal lung diseases (DPLDs). It defines the lung interstitium and its three subdivisions. It describes the approach to evaluating ILDs, which involves radiologists, pathologists and pulmonologists. ILDs can be classified as those of known cause, idiopathic interstitial pneumonias, granulomatous diseases, and other rare forms. Common idiopathic interstitial pneumonias are also outlined. The document reviews clinical assessment of ILDs including history, exam, imaging and lung function testing.