The Geo-Assessment Matrix (the Matrix) is a pan-European dataset highlighting the key geological features and associated engineering constraints for Offshore Wind Farm (OWF) development. Such geological features include: lithology; biogenic processes; mass flow processes; fluid flow; morphology and geomorphology associated with glacial, coastal, fluvial and marine settings. There is currently no universally adopted methodology or classification system to assess ground conditions at OWF sites. This lack of standardisation makes it difficult to compare siting conditions across different regions in Europe. The Geo-Assessment Matrix introduces a unified methodology designed to address these challenges. Results provide data attributions that can be used to create pan-European geological maps to better understand the geological constraints of the subsurface for offshore development. The Matrix is useful for stakeholders such as research institutes (Geological Surveys), marine spatial planners, government agencies and OWF developers. A matrix style is adopted providing a structured comparison of geological and engineering constraints for the development of different OWF foundation types (piles, suction caisson, gravity based structures – GBS, and cables). A final qualitative unmitigated geological constraint score is provided for evaluating the suitability of different seabed conditions: ‘Higher’, ‘Moderate’ and ‘Lower’ constraints. As this is a qualitative assessment, they are comparative terms, permitting categories that reflect the relative difference. - Higher constraint: Geological features may present significant challenges to engineering solutions. These are typically (but not limited to) geohazards, such as organic soils, pockmarks, active sedimentary systems, slope instability and soft sediments. - Moderate constraint: Geological features may be suitable for foundations, however, likely need additional engineering design/solutions mitigation measures. These are typically variable sedimentary features, such as heterogeneous sediments, mobile sediments, weak bedrock and gravel. - Lower constraint: Geological features are likely suitable for foundations. These are typically more predictable sediments, such as homogeneous or layered sediments or strong bedrock. Note that some features may still require mitigation measures. Outputs from the Matrix help to inform early decision-making and spatial planning by highlighting areas of relative geological constraint in countries during the early stages of offshore wind development.