Interstitial lung isease (ILD), also known as diffuse parenchymal lung disease (DPLD), refers to a group of lung diseases (including idiopathic pulmonary fibrosis), affecting the alveolar epithelium, pulmonary capillary endothelium, basement membrane, perivascular and perilymphatic tissues. The term ILD is used to distinguish these diseases from obstructive airways diseases. Most types of ILD involve fibrosis, but this is not essential; indeed fibrosis is often a later feature. Hence the term pulmonary fibrosis has fallen out of favor.