In paediatrics, the pulmonary function test (PFT) is most often performed to support the diagnosis or in follow-up of asthma patients. Whatever the pathology responsible for respiratory symptoms and/or functional impairment, repeated PFTs make it possible to establish a prognosis (pulmonary function trajectories…) and to orient preventive interventions. PFT can be performed routinely from the age of three years, provided that the following requirements are met: suitable techniques and equipment, staff trained to apply the techniques and to receive young children, reference values for each technique indicating the limits of normal values and of between-test significant variation. From the age of three, children can be subjected to tidal breathing measurement of: resistance of the respiratory system (oscillometry, Rrs; airflow interruption, Rint) or of airways specific resistance (sRaw) and functional residual capacity (by applying a dilution technique). With maturity, the child will become capable of mobilizing his or her slow vital capacity to measure total lung capacity (TLC), once again by applying a dilution technique, then later by breathing against a closed shutter (plethysmography TLC and Raw). Finally, the child will be able to carry out forced expiration (forced spirometry) along with all of the other PFTs. It is important to take into account the paediatric adaptations specified in the international recommendations regarding the performance, reproducibility and quality of PFTs targeting this population.