A large number of pathological situations can impair gas exchange and contribute to progressive lung damage and ILD. Consequently, diagnosis approaches need to be organized by cause, with a clinical evaluation requiring a careful history paying attention to exposures and systemic diseases. Indeed, in a number of pathological situations, no final diagnosis is proposed and the conclusion reported by the physician in charge of the patient is ILD of unknown cause. However, information from recent studies highlights the concept that lung insults caused by substances from the environment or in the context of systemic diseases are largely under-estimated and should be more often discussed considered in the diagnostic process. Based on this consideration, the following diagnostic grouping for pediatric ILD can be considered 1) exposure-related ILD; 2) systemic disease-associated ILD; 3) alveolar structure disorder-associated ILD; and 4) ILD specific to infancy.