There is an ethical requirement to avoid unnecessary studies in children. In addition, smaller patient populations, challenges with patient recruitment, trial design considerations, blood sampling volume limits, etc., underscore the need to optimize the collection, analysis, and interpretation of data in children. Pediatric extrapolation has evolved as an approach that allows leveraging of existing data to minimize data required from prospective clinical trials in children. The use of pediatric extrapolation is grounded in the confidence in similarity of the disease and response to therapy between a reference (usually adult) and pediatric population. As such, there is critical need to systematically assess assumptions around disease and response similarity. The goal of this presentation is to lay out the foundation of pediatric extrapolation and share cases that exemplify approaches used for assessing extrapolation assumptions and exploring trial designs for future pediatric development programs.