Impact evaluations can be an essential tool for determining if a specific program or activity had the desired effect. They can help to reveal what worked, or did not work, and why. But conducting such evaluations can be complex, costly, and time-consuming, placing a premium on proper preparation and identifying exactly which questions the impact evaluation will seek to answer. This case study provides lessons learned on identifying how, when, and why to conduct an impact assessment in large organizations with many, diverse program activities to produce high-quality evidence and ultimately inform policymaking.