Interstitial lung diseases ( ILDs) are a heterogeneous group of lung disorders with distinct clinical, radiological and morphological features. Among ILDs, idiopathic pulmonary fibrosis ( IPF) is associated with the worst prognosis, with a survival worse than many cancers, even after the advent of two anti- fibrotic drugs, shown to halve disease progression. Reaching the correct diagnosis is crucial, as pathogenesis, prognosis and treatment options differ substantially from other interstitial fibrosing processes where immune overactivity plays a role in driving fibrosis. However, a subgroup of patients with fibrotic lung disease mediated by immune dysregulation can experience relentlessly progressive fibrosis despite immunosuppressive treatment, and behave similarly to IPF. It is clear that even in non IPF ILDs, phenotypes of relentlessly progressive disease exist, and molecular pathways may overlap. One of the main challenges for the future is the use of high throughput molecular biology techniques to stratify patients with progressive fibrotic lung disease, in order to identify genetic, epigenetic and protein markers to predict the individual patient's rate of progression and fundamental molecular pathways involved. In this review, we will focus on the challenges in the diagnosis and management of idiopathic pulmonary fibrosis as well as differences and areas of overlap with other fibrotic ILDs, including fibrotic hypersensitivity pneumonitis, connective tissue disease- associated ILD and interstitial pneumonia with autoimmune features.