Lung fibrosis is a dysregulated or exaggerated tissue repair process resulting in the thickening or scarring of lung tissue. It involves the presence of sustained or repeated exposure to a stressor and intricate dynamics between several inflammatory and immune response cells, and the microenvironment of the alveolar-capillary region consisting of both immune and non-immune cells, and the lung interstitium. This AOP is applicable to a broad group of stressors of diverse properties e.g. metal dusts, pharmacological products, fibres, microorganisms, chemicals, including novel technology-enabled stressors such as nanomaterials. This AOP is referred to as AOP 173 in the Collaborative Adverse Outcome Pathway Wiki (AOP-Wiki).