[REPORT] Best Practices in Citizen Science for Environmental MonitoringThe volume of environmental knowledge generated by citizen science initiatives across the EU offers a unique opportunity to help deliver on the European Green Deal and other EU (and global) priorities, and to involve the public in EU policy-making. This document summarises the opportunities for and benefits of using citizen science for environmental monitoring, highlights good practices and lessons learnt, and identifies the obstacles holding back its broader uptake. On that basis, it puts forward recommendations and possible actions to facilitate and enhance the use of citizen science in environmental monitoring. Citizen science can be defined as the non-professional involvement of volunteers in the scientific process, commonly in data collection, but also in other phases, such as quality assurance, data analysis and interpretation, problem definition and the dissemination of results. This document does not cover their participation in opinion polls or personal data on participants and their views. Citizen science is a powerful tool for public engagement and empowerment in policy-making and for raising awareness of environmental issues and policies. By promoting people’s involvement in EU policies, the recommendations in this document contribute directly to the European Commission’s policies on open, transparent and participatory decision-making, such as ‘a new push for European democracy’ (one of its six headline ambitions 1 ), better regulation 2 , e-government digital single market), and the EU’s implementation of the Aarhus Convention 3and open data 4(the 5 .