Integrated care is a key strategy in reforming health systems around the world. Despite its importance, the concept's polymorphous nature and lack of specificity and clarity significantly hamper systematic understanding, successful application and meaningful evaluation. This article explores the many definitions, concepts, logics and methods found in health system and service integration. In addition to framing this evolving, albeit imprecise field, the article summarizes the main elements or building blocks of integrated care and suggests a way to address its various complexities and unknowns in a real-world sense.