Interstitial lung disease (ILD) in infants and children represents a heterogeneous group of respiratory disorders that are mostly chronic and associated with high morbidity and mortality. Typical features of ILD include dyspnoea, the presence of diffuse infiltrates on chest radiographs and abnormal pulmonary function tests with evidence of a restrictive ventilatory defect (in older children) and/or impaired gas exchange. ILD is difficult to diagnose, as no classification scheme is entirely satisfactory. Recently, it has been proposed to categorise paediatric ILD as either primary pulmonary disorders or systemic disorders with pulmonary involvement. However, this classification leaves the difficult problem of which clinical conditions should be included or excluded in infants and children. The present article reviews interstitial lung disease in infants and children, placing emphasis on current concepts of pathophysiological mechanisms and approaches to treatment.