peer reviewed ; This paper examines the question of sustainable consumption through the consumer’s contribution to the various dimensions of sustainability. The consumer’s participation reveals legitimacy conflicts in the process of designing new production systems. The different dimensions of sustainability can be linked to different legitimacy models. When the building of new systems entails a concerted process involving dialogue and deliberation among stakeholders from the agricultural and environmental sectors, various legitimacy principles are mobilized and confront each other through the spokespeople who represent the interests involved. This specific case concerns beef produced from the ”Gaume grassland steer,” a system that can be characterized as agroecological and territorial. The consumers who were involved contributed, through deliberative processes, to the coexistence of various legitimacy principles and stakeholder cooperation. This capacity could be linked to their multiple and fuzzy identities because their identities were shown to be flexible, changing with the institutional setting, which was sometimes consumer-oriented and sometimes territory-driven. This allowed them to act as mediators between environmentalists and farmers. To do this they had to be able to accept the limits of each legitimacy principle and contest the possibility of imposing only one principle on all the others. In so doing they helped the heterogeneous actors to reach compromises by referring to a kind of patrimonial common good.