Interventions to transform the delivery of health are being implemented widely. Assessing the impact of these health interventions enables healthcare teams to learn and to improve services and can inform future policy. A health intervention is a combination of activities or strategies designed to assess, improve, maintain, promote, or modify health among individuals or an entire population. An impact evaluation is a systematic and empirical investigation of the effects of an intervention; it assesses to what extent the outcomes experienced by affected individuals were caused by the intervention in question and what can be attributed to other factors such as other interventions, socioeconomic trends, and political or environmental conditions. A range of routinely collected administrative and clinically generated healthcare data could be used to evaluate the impact of interventions to improve care. This process can help inform health promotion policies and practices. The chapter introduces healthcare professionals, wishing to perform an impact evaluation of a health intervention, the key concepts and steps relating to design, analysis, and implementation.