Citizen science has manifold relationships to policy, which is understood as sets of ideas or plans for action followed by a government, business, political party, or group of people. In this chapter, we focus on the relationship between citizen science, government policies, and the related notions of politics and polity. We discuss two core areas of interaction between citizen science and policy. Firstly, government policies can support citizen science to flourish, for example, through legitimisation or funding. Secondly, citizen science can contribute to policymaking at various stages of the policy cycle, including policy preparation, formulation, implementation, monitoring, and evaluation. Since both of these perspectives are intertwined, the policy landscape related to citizen science is complex, and it is continuously evolving. This chapter disentangles some of the complexities, with a particular focus on the European landscape, its geographic diversity, and key players (stakeholders and beneficiaries). It presents a brief history and the current context and also includes recommendations for the future with respect to governance, policy impact, sustainability of citizen science initiatives, and the role of digital transformations. We showcase the pathways of leading examples but also highlight currently unanswered questions.