Risk stratification has proven of value in adjusting the doses of adjuvant chemotherapy and deciding on radiation therapy when treating children with a variety of solid tumors. It enabled childhood cancer treatment to be fine-tuned to maximize the chance of long-term cure, while at the same time minimizing the risk of treatment toxicity and late effects. While the paradigm of evaluating the impact of neoadjuvant chemotherapy to intensify or cut back on treatment is well-established, it is also becoming clear with the passage of time that it occupies a position in determining therapy that is increasingly nuanced. It is important for the surgeon to understand how response assessment can be of benefit, even helping to guide when surgery should be performed, and identifying where it is of less certain value in impacting ongoing treatment, rather than being used in a clinical trial setting where reduction of treatment is being contemplated to mitigate late effects. In this chapter we will look at how response is measured for various pediatric solid tumors, the background of how such assessment came about, where response measurement provides benefit, and how surgeons need to thoughtfully interpret such data for each patient to ensure the maximum chance of long-term remission.