Citizen science in Croatia has developed intensely over the past decade, growing from isolated, mostly environmental initiatives to a structured movement in which libraries take the lead role as intermediaries between the scientific community and the general public. Libraries are particularly well positioned for this role, combining public trust, educational mission, access to collections and digital infrastructures, and long-term institutional capacity for sustaining community engagement. Within the Croatian context, this strategic positioning allows libraries to act as vital bridges between science and society, effectively operationalizing citizen science hubs.

A descriptive case study of the National and University Library in Zagreb (NSK) serves to illustrate how a library can function as both an initiator and a hub of citizen science. Based on project documentation and institutional reports, the study examines the implementation processes, challenges, and outcomes of NSK’s citizen science initiatives.

The National and University Library in Zagreb (NSK) recognized the potential of this model early on, transitioning into a national leader for citizen science through its participation in the international Erasmus+ project CeOS_SE (Citizen-Enhanced Open Science in Southeastern Europe), which ran from 2022 to 2024. Coordinated by LIBER Europe (Association of European Research Libraries), this project aimed to establish research libraries as knowledge hubs for open and citizen science. Within this framework, NSK implemented two foundational pilot activities: the Bees, Life, People project, a landmark collaboration between NSK, the Ivanić-Grad Public Library, and the Croatian Web Archive (HAW), and the Self-Help and Well-Being in the Academic Online Environment activity conducted with students from the Faculty of Humanities and Social Sciences in Zagreb. These activities show that citizen science in libraries can connect environmental monitoring, digital heritage, and academic learning in one institutional setting.

NSK has continued to solidify its role through specialized projects that bridge cultural heritage and modern technology. Notable initiatives include Dendroteka, HAWathon, and Musical Intelligence in the Service of National Heritage. Dendroteka highlighted the intersection of ecological monitoring and citizen engagement by involving the community in collecting data about tree species and urban greenery. HAWathon represents a specialized “marathon” in web archiving, engaging students in the systematic selection and preservation of digital content and ensuring that

ephemeral web data is saved for future research. Musical Intelligence in the Service of National Heritage is a pioneering project exploring the synergy between citizen science and Artificial Intelligence by engaging volunteers in processing or categorization of musical heritage.

A cornerstone of NSK’s strategy is the development of robust institutional partnerships. This is most evident in its collaboration with the Working Group for Citizen Science in Libraries (GZUK) of the Zagreb Library Association, which serves as a platform for connecting different types of libraries in community-driven science. A key current collaboration is the ongoing project “BioBlitz and Libraries”. This joint initiative represents the next phase of institutional synergy, attracting more than 60 libraries across Croatia and demonstrating the capacity of the library network to conduct large-scale environmental monitoring and data collection.

Through these diverse efforts, NSK has positioned itself as a central institution for providing specialized education on citizen science for both libraries and the scientific community, with plans to extend these programs to library users in the near future. Beyond practical implementation, the Library acts as a consultancy hub, advising other organizations on how to design and manage citizen science activities. Addressing the challenge of sustainability, these initiatives transition from temporary, project-funded activities, such as those under the CeOS_SE project framework, into permanent institutional practices by integrating citizen science into regular programs and leveraging existing library infrastructure and networks. By simultaneously conducting original research and expanding the theoretical framework of citizen science within librarianship, NSK ensures that its work is deeply rooted in both practice and academic theory. This dual approach supports a sustainable ecosystem that bridges national expertise with grassroots professional networks and strengthens the future of open and citizen science in Croatia.