Some policy-oriented concepts such as Ecosystem Services (ESS) remain widely utilized, despite obvious difficulties in operationalizing them. How does the concept persist? In a large EU Horizon 2020 project, researchers from different institutes worked together to develop an indicator of the environmental performance of agricultural practices, expressed in terms of ESS. Two observations of this project help to explain how ESS are progressively turned into a socially shared concept that may transform its environment and perpetuate itself. Firstly, the challenges of operationalizing ESS facilitated the formation of a group of researchers dedicated to the concept. As the project advanced, researchers progressively cut ties with the environmental sciences on which ESS are meant to be based. The interpretive flexibility of the ESS concept contributed to shaping the socially shared reality within which it was situated. Secondly, the legal obligations and procedures of the Horizon 2020 project were an essential factor for the constitutive strength of the ESS concept. As a straitjacket, the grant agreement ensured that the project maintained the researcher-indicator relationship. Thus, researchers were persistently oriented towards developing and expanding the ESS concept. This case illustrates how a research project can be formed and maintained around relatively ill-defined concepts in large consortia that are meant to produce policy-relevant science.