The interstitial lung diseases are a heterogeneous group of disorders characterized by inflammation and/or fibrosis of the pulmonary interstitium. In 2002, the American Thoracic Society and the European Respiratory Society revised the classification of interstitial lung diseases and introduced the term diffuse parenchymal lung disease. The idiopathic interstitial pneumonias are a subtype of diffuse parenchymal lung disease. The idiopathic interstitial pneumonias are subdivided into usual interstitial pneumonia (with its clinical counterpart idiopathic interstitial pneumonia), nonspecific interstitial pneumonia, cryptogenic organizing pneumonia, acute interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, and lymphocytic pneumonia. Sarcoidosis and hypersensitivity pneumonitis are the 2 most common granulomatous diffuse parenchymal lung diseases. Rheumatoid arthritis, systemic sclerosis, and dermatomyositis/polymyositis (causing antisynthetase syndrome) are diffuse parenchymal lung diseases of known association because these conditions are associated with connective tissue disease. Hermansky-Pudlak syndrome is a rare genetic diffuse parenchymal lung disease characterized by the clinical triad of pulmonary disease, oculocutaneous albinism, and bleeding diathesis. This review provides an overview of the chronic fibrosing diffuse parenchymal lung diseases. Its primary objective is to illuminate the clinical challenges encountered by clinicians who manage the diffuse parenchymal lung diseases regularly and to offer potential solutions to those challenges. Treatment for the diffuse parenchymal lung diseases is limited, and for many patients with end-stage disease, lung transplantation remains the best option. Although much has been learned about the diffuse parenchymal lung diseases during the past decade, research in these diseases is urgently needed.