There is increasing recognition of the need for objective physiological measurements of lung function during the preschool years in order to identify and treat early lung disease before irreversible structural changes occur; monitor disease progression and efficacy of therapeutic interventions and distinguish the various wheezing phenotypes that occur in this age group, all of which require different management strategies. While preschool pulmonary function tests are undoubtedly excellent research tools , their role in the clinical management of the individual young child remains more controversial . In particular, further work is required to establish information on the within -subject , between occasion variability and the relative sensitivity and specificity of each technique, as well as developing more appropriate prediction equations for this age group, before they can be used confidently in the clinical management of individual child. This review examines the various challenges facing paediatricians who are responsible for children with respiratory diseases such as asthma, wheezing, cystic fibrosis and chronic lung disease following preterm delivery and summarises recent recommendations from an ATS/ERS Task Force.