Can public libraries become hubs for citizen science? We answer this question collaboratively, in line with citizen scienceprinciples. Two hands-on activities for librarians of the Barcelona Network of Public Libraries were ideated and implemented. One was a training course for 30 librarians from 24 libraries. The training empowered the librarians and allowed them to envisage citizen science tailormade implementation in each library. The second activity consisted of the co-creation of a citizen social science project. 40 library users, 7 librarians from 3 different cities, and professional scientists, were involved. Before, during and after the activities, we listened to librarians and users with participant observation, surveys, and a focus group to identify strengths and challenges. The potential of citizen science at public libraries, and especially its co-created citizen social science format, lays within a more social dimension that allows to strengthen social bonds among participants andacquire better knowledge of the environment. However, the potential may be hindered by the complexity of collaboration, the uncertainty of research co-creation and by participant retention strategies. The results overall suggest that public libraries can offer leadership in the promotion and implementation of citizen science initiatives, contributing to the debate over the public libraries’ mission as local community hubs.