What explains variation in use of health services and perception of health outcomes? Answering such causal questions is hard to do credibly and cost-effectively. This chapter presents the Qualitative Impact Protocol, an approach to impact evaluation based on collecting narrative data directly from stakeholders about the changes they perceive to be most important in explaining outcomes across multiple domains relevant to an intervention’s goals. The chapter demonstrates how data can be coded and visualized using causal mapping. Findings can contribute both to developing and to testing theories about the causal mechanisms explaining people’s behavior.