Despite governmental and international funding as well as numerous publications on health systems, questions remain. João Costa offers new insight into health systems thinking by emphasizing the social nature of health systems. He traces health systems back to their origins in Ancient Greece and investigates their development throughout history, focusing on the notion of systems' self-reference, a constitutive feature of social systems. The study is built on Luhmann's Social Systems Theory and his outline of health as social system. Valuable for health professionals, it discusses communication as lifeblood for making health systems self-referential.