We aim to establish a pan-European research infrastructure (RI) for excellent and impactful citizen science to optimise effectiveness, scaling-up and ensure sustainability for any initiative.

With this position paper, we urge decision-makers and funders to support the establishment of a this RI that may centralise and provide open resources and services without charge, based on excellence criteria. We also review here various aspects when co-designing its scientific, technological, and governance models from the very early conceptual and planning stage.  After a period of continous growth in number, nature and impacts of citizen science initiativies, main current challenges are persistent fragmentation, short-term funding, and duplication of efforts that impede efficiency, sustainability and excellence. The time to act is now.