[Departement_IRSTEA]RE [TR1_IRSTEA]GES / USAGESFour examples of evaluation are presented concerning policies implemented by the Water agency Seine-Normandie in France. We analyse whose legitimacy supported such evaluation and conclude that three main types of legitimacy are to be considered. The manager takes upon himself/herself a personal interpretation of his/her mandate and is legitimate for assessing performances according such definition of the public mission. Social concerns evolve and society is legitimate in demanding accountability of public institution and asking to what extent present concerns are taken into account. But society is plural and contradictory. Therefore several partisan evaluations are legitimate to question public...