In the shadow of the deployment of instruments inspired by the logic of New Public Management, indicators designed to assess hospital quality have become widespread over the last fifteen years. This article focuses on the indicators legitimizing activities of various experts: management researchers, experts within hospital federations, medical learned societies or regional evaluation bodies. Situated at the interface between hospital administration and local hospital worlds, these experts constitute an interconnected nebula of multi-positioned actors, which has actively contributed to the institutional integration of the sector.