Financial markets, actors, institutions and technologies are increasingly determining which kinds of services and ’welfare’ are available, how these are narrated, and what comes to represent the ’common sense’ in the policy world and in everyday life. This Element problematises the rationale and operation of one such financial technology, private health insurance, and the industry it inhabits. It offers a cross-disciplinary overview of the various drivers of these markets in middle-income countries and their appeal for development institutions and for governments. Using a range of illustrative case examples and drawing on critical scholarship it considers how new markets are pursued and how states are entangled with market development. It reflects on how the private health insurance sector in turn is shaping and segmenting health systems, and also our ideas about rights, fairness and responsibility.