In 2018, the Université de Lorraine (UL) laid the foundations for its Open Science (OS) policy by making its open repository the institution’s official bibliography. Today, it is involved in all OS areas: scientific publishing, research data, codes and software, bibliometrics. It has achieved this first and foremost through a solid political will, structured in one OS steering committee and three operational committees led by the Open Science vice-president. Comprising researchers, information professionals, IT specialists and legal experts, they lead the university’s OS policy. UL published a series of positions to encourage good publication practices, advise against the payment of Article Processing Charges, take a political stand on the so-called transforming agreements and support the Right Retention Strategy. To support its decisions, UL made engaging financial choices. The university withdrew from Springer deal in 2017, then from Wiley deal in 2023. The funds released have been allocated to an annual support fund for OS infrastructures (€100,000), which helps major players in open scholarly communication like the DOAJ, Erudit and OpenEdition. The institution also provides financial aid (€30,000) for the continued existence and creation of diamond journals such as Philosphia Scientiae. At the same time, UL has set up services and an internal professional network to support its researchers’ publishing initiatives. The university presses publish all books on Open Monograph Press with immediate open access while the journal publishing service supports the creation of new diamond journals. The publishing staff network brings together researchers, publishers and librarians to encourage the transition of the university’s publications to the diamond model. In five years, the Université de Lorraine has built up a robust policy to support Open Science, and more particularly open scholarly communication, based on three pillars: a firm political will, clear budgetary guidelines and the deployment of support services.