This study reviews the status of Marine Biodiversity Monitoring in the European Union (EU) and its adjacent waters building on work by EuropaBON, EuroSea and other projects. The study established definitions of the approaches used in the EU for marine biodiversity monitoring and identified 220 stakeholders, representing 22 EU countries. Subsequently, 647 distinct biodiversity monitoring programmes that undertook consistent sampling in EU marine waters were identified, and the employed and/or emerging methodologies used were summarized. A total of 41 data collection frameworks and portals were identified and categorized, 14 of which cover Europe. Research projects were also contemplated and following a review of approximately 600 research projects, 95 were found to be relevant and further analyzed. Overall, we identified significant marine biodiversity monitoring efforts across the EU but also mismatched in the spatial/taxonomic distribution and scale of effort. These gaps need to be addressed to achieve a comprehensive EU-wide marine biodiversity monitoring system, which outputs should follow the FAIR principles. We recommend drawing on the results of this study to establish a more coordinated effort of marine biodiversity monitoring in Europe, in collaboration with ongoing efforts by EuropaBON, MBON, GOOS and the European initiative for Ocean Observation. Files: MarBioME Final Report to the European Commission. Overview and assessment of the current state of Marine Biodiversity Monitoring in the European Union and adjacent marine waters (RTD/2021/MV/11). MarBioME Executive Summary to the European Commission. Overview and assessment of the current state of Marine Biodiversity Monitoring in the European Union and adjacent marine waters (RTD/2021/MV/11). MarBioME Résumé Excecutif pour la Commission Européenne. Aperçu et évaluation de l'état actuel de la surveillance de la biodiversité marine dans l'Union Européenne et les eaux marines adjacentes (RTD/2021/MV/11). Annexe 1. Task 1. The terminology used and a brief historic framework Overview of definitions of marine biodiversity monitoring, description of the current state of implementation of marine monitoring in the EU and its organisational and technical set-up (Word doc). Annexe 2. Task 1. MarBioME Stakeholders database Mapping of actors involved in marine biodiversity monitoring in the EU is available in the form of Excel tables. Annexe 3. Task 1. MarBioME Geospatial information Mapping of actors involved in marine biodiversity monitoring in the EU structured in shapefile format, a simple and non-topological format for storing the geometric location information and the attributes of the geographic features related to the task. Annexe 4. Task 2. Monitoring Programmes Analysis of the spatial and temporal monitoring coverage of marine species and habitats in the EU, according to identified monitoring programs (Excel Sheet). Annexe 5. Task 2. Interactive Map App According to identified monitoring programs, map with a georeferenced analysis of the spatial and temporal monitoring coverage of marine species and habitats in the EU. Annexe 6. Task 2. Spreadsheet linking script with a readme Programme design metadata and accompanying spatial data are presented in filterable linked spreadsheets. Annexe 7. Task 2. European subset of BioTIME database European subset of time-series biodiversity database. Annexe 8. Task 3. Monitoring Standard Operating Procedures Summary of the marine biodiversity monitoring methodologies and protocols currently employed in the EU as well as emerging methods and technologies, according to identified monitoring programs (Excel sheet). Annexe 9. Task 3. Programme methods Detailed methodologies provided by individual EU countries, available in Word doc. Annexe 10. Task 4. Data Collection Frameworks Summary of marine biodiversity data collection frameworks and databases that integrate the outputs of European monitoring programmes, available in an Excel sheet. Annexe 11. Task 5. Research Projects Excel spreadsheet with an analysis of biodiversity monitoring research projects in the EU, including involved actors; spatio-temporal distribution; monitored taxa groups and ecosystems and project objectives addressed. Annexe 12. Task 7. Data extraction of Research Projects Comprehensive analysis and identification of research gaps (spatial, temporal and taxonomic) in the current marine biodiversity monitoring in the EU, in the form of a table overview.