This chapter provides an overview of fibrosing interstitial lung disease (ILD), a broad group of over 200 lung conditions, some of which can progress to severe, irreversible fibrosis. ILDs can have various causes, ranging from environmental exposures to autoimmune diseases, and while some may be treatable or reversible, others, such as idiopathic pulmonary fibrosis (IPF), lead to significant lung damage and poor outcomes. Lung fibrosis occurs when abnormal tissue repair leads to scarring, impairing the lungs’ ability to function properly. The chapter emphasizes the importance of chest CT scans in diagnosing and evaluating lung fibrosis, highlighting common imaging patterns such as honeycombing, traction bronchiectasis, and architectural distortion. Identifying these patterns is critical to diagnose different types of ILDs. The chapter also discusses several common fibrosing ILDs, including IPF, nonspecific interstitial pneumonia (NSIP), sarcoidosis, and hypersensitivity pneumonitis (HP). Each disease has distinct clinical and imaging features, though some, such as chronic HP and IPF, can appear similar, making diagnosis challenging. A systematic, multidisciplinary approach, involving specialists such as radiologists and pulmonologists, is key to accurate diagnosis and effective management of these diseases.