To achieve ambitious energy efficiency objectives, large public institutions face challenges to embark employees and building users. In this regard the French Social Security deploys actions to raise awareness among a large number of internal stakeholders, in order to increase acceptance, participation and responsibility to bring about behavioural change on energy efficiency. The paper presents the results of the programme Impulsion2021, a large-scale awareness-raising program which targets

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... employees. The program consisted of several phases: a) identify participants, b) develop learning material, c) plan and execute the communication campaign d) facilitate internal communities, and e) measure and analysis of participatory results. A specific focus on the adaptation of learning programs is presented: one program targeted for general users on daily actions, and another targeted to professionals responsible of building operations and renovation actions. The results show an increased level of participation during the program, as measured by the increased level of interactions on the topic within the internal communication channels, and the exchange of over 50 best practices carried out throughout the institution. The experience shows the opportunities and impact of a common and long-term awareness program and its potential influence on daily behaviour of users. Finally, the program managed to mobilise an unprecedented number of people, which has encouraged the institution to evaluate its continuity.