This policy brief examines how government authorities at all levels can strengthen cooperation with Citizen Observatories (COs) — participatory initiatives in which residents, community groups, municipal staff, and researchers jointly monitor the local environment and co-create solutions. It argues that COs offer data and perspectives often unavailable through conventional monitoring, supporting policy responses to climate change, air pollution, biodiversity decline, and the urban green transition. Drawing on examples from Rotterdam, Barcelona, Kristiansand, and Athens, the brief identifies key social and technological barriers to effective cooperation — including data quality, interoperability, and inclusion — and presents good practices for addressing them. It concludes with three recommendations for policymakers: developing governance frameworks for collaboration, providing shared infrastructures and data-gathering support, and ensuring inclusive participation, including engagement with the creative sector. The brief draws on tools and practices developed through the CitiObs project. Gold, M., Castell, N. Volten, H., Verhoeven, E., Guy Jessica, Castell, N. Heikkilä, S. 2026. Cooperation with Citizen Observatories: addressing social and technological barriers. CitiObs Policy Brief