Citizen science is increasingly upheld with the potential to underpin all aspects of the environmental policy process. However, to date, contributions of citizen science to environmental decision-making remain sparse and not well understood. Evidence points to a gap between the potential relevance of citizen science for policy and its actual implementation. We lack a comprehensive assessment of the current impacts of citizen science projects on environmental policy, and an identification of the scientific, engagement, and governance characteristics of projects that facilitate successful contributions to policy. This paper addresses that knowledge gap through identifying the characteristics of citizen science projects that support policy. We present an inventory of 503 citizen science projects with environmental policy relevance, and an in-depth analysis of 45 case examples with quantitative assessment of characteristics of the citizen scientist, scientific, socioeconomic , and policy dimensions. Our results demonstrate that citizen science can underpin all steps of the environmental policy process, and that a diversity of approaches can be used to achieve this. However, governmental support, scientific excellence, and NGO-leadership facilitate policy linkages. We discuss the main challenges and opportunities identified by project leaders in linking citizen science and policy and present a set of recommendations for promoting the better integration of citizen science in the different phases of the policy cycle. Central among these are clarifying policy needs, facilitating access to citizen science data, and improving their evaluation and recognition by decision-makers.

Success stories of citizen science projects widely demonstrate the value of this open science paradigm and encourage organizations to shift towards new ways of doing research. While benefits for researchers are clear, outcomes for individuals participating in these projects are not easy to assess. The wide spectrum of volunteers collaborating in citizen science projects greatly contributes to the difficulty in the evaluation of the projects' outcomes. Given the strong links between many citizen science projects and education, in this work we present an experience with hundreds of students (aged 15–18) of two different countries who participate in a project on cell biology research — Cell Spotting — as part of their regular classroom activities. Apart from introducing the project and resources involved, we aim to provide an overview of the benefits of integrating citizen science in the context of formal science education and of what teachers and students may obtain from it. In this case, besides helping students to consolidate and apply theoretical concepts included in the school curriculum, some other types of informal learning have also been observed such as the feeling of playing a key role, which contributed to an increase of students' motivation.

Citizen observatories (COs) have emerged as essential research infrastructures for participatory science, supporting data collection and community engagement. They enable communities to monitor their environments, actively track indicators aligned with the Sustainable Development Goals (SDGs), and contribute valuable data to scientific research and evidence-based, informed policy-making. Despite their growing importance, COs remain conceptually fluid, with varying interpretations across disciplines and contexts. This paper examines the evolution of COs from their origins in the early 2010s to their current multifaceted roles, revealing three key dimensions: descriptively as socio-technical systems, instrumentally as research infrastructures, and normatively as advanced participatory science initiatives. We specifically highlight the critical role of COs as research infrastructures and propose a set of essential functions and characteristics. These functions range from providing technical capabilities for data collection and quality assurance to social dimensions, including community building and governance frameworks. Additionally, our analysis identifies two operational models: tailored COs designed for specific projects and open COs supporting multiple initiatives. Reframing COs as research infrastructures rather than isolated initiatives emphasizes the need for long-term institutional support, shared services, and coordinated policies to ensure their sustainability and maximize their contribution to both scientific knowledge and public participation, ultimately strengthening the foundations of participatory science.

Citizen observatories (COs) have emerged as essential research infrastructures that support data collection and community engagement in participatory sciences, empowering communities to monitor their environments while generating valuable data for scientific research and policy-making. Despite their growing importance, COs remain conceptually fluid, with varying interpretations across disciplines and contexts. This paper examines the evolution of COs from their origins in the early 2010s to their current multifaceted roles, revealing three key dimensions: descriptively as socio-technical systems, instrumentally as research infrastructures, and normatively as advanced participatory science initiatives. We specifically highlight the critical yet underexplored role of COs as research infrastructures and propose a set of essential functions and characteristics that define COs in this infrastructure role. These functions range from providing technical capabilities for data collection and quality assurance to social dimensions including community building and governance frameworks. Our analysis identifies two operational models: tailored COs designed for specific projects and open COs supporting multiple initiatives. Reframing COs as research infrastructures rather than isolated initiatives emphasizes the need for long-term institutional support, shared services, and coordinated policies to ensure their sustainability and maximize their contribution to both scientific knowledge and public participation, ultimately strengthening the foundations of participatory sciences.