The interstitial lung diseases are a group of disorders that predominantly, but not exclusively involve the lung interstitium. The lungs are affected in three ways. The lung tissue is damaged in some known or unknown way, followed by inflammation of the alveolar wall, and finally there is fibrosis in the interstitium that results in end stage lung. The stiff lungs cause a restrictive type of functional abnormality and affect gas exchange. ILD is a misnomer as the disorders actually involve the alveolo-capillary membrane, which includes the pulmonary interstitium, the alveolar epithelium and the capillary endothelium. The most common known causes are those related to occupational and environmental exposures and associated with connective tissue disorders such as rheumatoid arthritis and scleroderma. Despite significant improvement in our knowledge of pathogenesis of ILD, the etiology of a large number of cases remains unknown In recent times this group of disorders are classification to include acute interstitial pneumonia, a rapid fulminant form with poor response to therapy and about 90% mortality, usual interstitial pneumonitis UIP/idiopathic pulmonary fibrosis (IPF), desquamative interstitial pneumonitis and non-specific interstitial pneumonitis. These together form the group idiopathic interstitial pneumonias. UIP/idiopathic pulmonary fibrosis also called cryptogenic fibrosing alveolitis is the commonest condition seen in clinical practice. The pathogenesis, clinical features, diagnosis, radiological features, treatment, prognosis, and recent advances of IPF are discussed in detail.