This paper aims to probe what it sees as a woefully under-explored area: the differences between the United Kingdom’s four separate health systems. These systems, it argues, are diverging in terms of structures, management approaches, and the way social care relates to health. In theory, this divergence should offer a unique opportunity to establish ‘what works’ in these different approaches. In practice, the exercise is hampered by hard-to-compare data and a political reluctance to back comparative studies. Much more could be done to facilitate such studies.