Realist research and evaluation methods, including integrated care endeavors, are increasingly used in health and social care research settings. The realist view of how the world is and how we can explain it seeks to look ‘beneath the hood’ and to ask the questions of how and why. Health and social policy and service settings, within which integrated care strives to make a difference, are complex ‘open’ systems that can only partially be understood using empirical methods alone. Abductive and retroductive modes of reasoning, as used by realist researchers, are commonly used by physicians, detectives, and lawyers to postulate hidden explanations based on available experienced evidence. The approach is, therefore, not foreign to many readers of this chapter, and realist scientific methodology gives validity to this common but scientifically neglected mode of analysis.