Extrapolation of data is common in drug development. Policy makers such as NICE routinely extrapolate findings from clinical trials to wider populations; efficacy can be extrapolated across treatments shown by bioequivalence studies to have similar pharmacokinetic profiles. Extrapolating relevant data from a source population to a target population means that smaller trials in the target population may suffice to demonstrate efficacy, or additional trials may even be rendered unnecessary. A recent EMA concept paper outlines a framework for extrapolation in drug development. The potential for extrapolation to reduce the experimental burden in children is well recognised. However, significant assumptions are required regarding similarity in source and target populations, particularly where the former is adult and the latter paediatric, in order that extrapolations have biological plausibility. This project aims to identify current practices and statistical methods that can be used to optimise extrapolations in paediatric development programmes.