Challenges for behaviour change: 16 Challenges for policy change: The science-policy interface is complex, and many factors contribute to whether results of a citizen science initiative are adopted by policy stakeholders and lead to policy change. Some of these challenges are listed below: • There is a lack of alignment between research, community, and policymakers. This often translates into a mismatch between citizen science data and policy questions, goals and actions on the ground, scientific and political processes in timing and aptness of data to a specific policy process, i.e., public consultation, time cycles, and data infrastructures. Citizen science projects are often short-lived or cease to exist if they don’t achieve their desired outcomes, and data can sit on a website and reside there silently without being used by the public or government. • There is a power imbalance, so there is a need to share power and be aware of political biases. Most policymaking is still top-down, and evidence-based often excludes citizen science. • There are conflicting interests or goals of policymakers, citizen scientists and researchers from citizen science projects. • Divergent legislation and cultures across science and governance levels hamper the spread of knowledge and uptake of citizen science. • Civil servants who want citizens engaged in data collection practices often do not trust the data they collect. • Connecting citizen science with collaborative policymaking processes such as public consultations and citizen-initiated policy proposals is difficult. • The lack of resources such as funding, time and expertise hinders policy impact. • There is a high level of distrust and lack of mutual understanding between scientists, politicians, and citizens scientists. Civil servants and public officials who would like to have citizens engaged in data collection practices or citizen science often do not trust the quality (robustness, reliability, safety, and representativeness) of the collected data nor the approach itself as they fear political biases. • There is a lack of awareness about the benefits of citizen science or even about the breadth and diversity citizen science has to offer. • A significant proportion of citizen science projects’ impacts, including policy change impacts, happens after the lifetime of the projects and their funding period. It is therefore challenging to measure such changes. • Funding streams are a key for the success of any project. Some projects are in a ‘proof-of-concept’ phase and therefore depend on external funding to sustain their operations before generating sufficient income. In contrast, other projects risk stopping if the external funding from donors and development agencies runs out. Projects thus must explore different revenue strategies and diversify their income streams.