As part of the European Data Strategy towards establishing a Single EU Market for data, the European Commission is working on common European data spaces including a Green Deal Data Space (GDDS) that covers issues such as climate change, circular economy, pollution, biodiversity and deforestation. The successful development of the EU GDDS will depend on the availability of FAIR (findable, accessible, interoperable and reusable) data sources, including FAIR volunteered geographic information and citizen science data. Active citizen engagement in science is now one of the European Research Area priority actions, as defined in the Pact for Research and Innovation (R&I) in Europe. The Open Science Policy of the European Commission recognises Citizen Science as one of its eight policy ambitions, stating that “the general public should be able to make significant contributions and be recognised as valid European science knowledge producers”. This document is the Deliverable 2.3 for the AD4GD project. It presents the results achieved in the context of Task 2.2 “Identification of CitSci data including complementary socioeconomic and INSPIRE data” as part of Work Package 2 “In-situ networks, CitSci and Socioeconomic Data”. The reader should consider that a follow-up version of this document will be released on month 30 of the project as Deliverable 2.4. This document offers a review of the current state of play with citizen science data in regard to FAIR compliance. It highlights citizen science initiatives that successfully apply open standards and tools to collect and share data that closely align with FAIR data principles and is a potential candidate for the inclusion into the EU GDDS. It examines platforms and tools that can support citizen science projects and discusses gaps that still exist to achieve citizen science data FAIRness.