Interstitial lung diseases (ILD) encompass a large number of conditions, with a wide range of causes, clinical manifestations, and imaging and pathological features. Most of the ILDs share pathologic abnormalities predominating in the lung interstitium, which is infiltrated by various combinations of inflammatory cells and fibrosis. Despite the intrinsic heterogeneity of this group of diseases, a large proportion of ILDs are fibrotic [1], i.e. associated with excessive deposition in the lung interstitium of extracellular matrix. Fibrotic ILDs may be limited to the lung as in idiopathic pulmonary fibrosis, or may occur in the context of underlying systemic disease especially sarcoidosis and connective tissue disease (CTD). Sarcoidosis–associated ILDs, CTD-ILD, and idiopathic pulmonary fibrosis are the most common fibrotic ILDs, with an estimated prevalence of 30.2, 12.1, and 8.2 cases per 100,000, respectively.