This poster presents the community-driven process behind the establishment of the Croatian Centre for Diamond Open Access, an initiative rooted in Croatia's long-standing tradition of non-commercial, scholar-led publishing.Diamond Open Access in Croatia did not develop from a policy mandate but as a practice sustained for decades by editors, libraries, universities, and information technology experts. Building on this tradition, members of the OPERAS-HR consortium signed a Memorandum of Understanding in 2025 to formalise collaboration and strengthen national coordination. The signatories include the University of Zadar (OPERAS National Node for Croatia), the University of Zagreb University Computing Centre (SRCE), the University of Zagreb Faculty of Humanities and Social Sciences, the Croatian Association for Scholarly Communication (ZNAK / CROASC), and the National and University Library in Zagreb (NSK).The creation of the Centre is part of the broader European effort led by the European Diamond Capacity Hub (EDCH) to consolidate and support the Diamond OA ecosystem. Rather than building something entirely new, the Croatian initiative connects existing expertise, infrastructures, and communities into a more visible and sustainable network.The Croatian Centre for Diamond Open Access will act as a coordination and support hub for Diamond OA journals and books. Its role is to strengthen editorial quality, provide training and shared services, encourage sustainable funding models, and align national practices with European guidelines and the Croatian Open Science Plan, while preserving the community-led character of Croatian publishing. The poster outlines the Centre's collaborative governance model, planned activities, and sustainability approach, highlighting how a strong scholarly community can move from informal cooperation to structured coordination.