Pulmonary fibrosis is a diverse group of lung disorders defined by varying degrees of fibrosis and inflammation in the pulmonary parenchyma. While it may be caused by a known disease, e.g., autoimmune or connective tissue disorder, drugs, hypersensitivity to inhaled organic antigens, or sarcoidosis, it also occurs to be idiopathic. When we examine the pathogenesis of lung fibrosis, we see that cellular aging plays a major role. Lung fibroblasts play an active role in the regeneration process. However, despite all the information, the pathogenesis of lung fibrosis is not clearly understood. It is not yet clear how senescent cells in the lung mingle and cause fibrosis. The pathogenesis of lung fibrosis will be understood more clearly following future studies.