This report is a knowledge synthesis, commissioned by the European Commission’s Directorate-General for Environment (DG ENV), conducted by Eklipse under the EU-funded BioAgora project “Connecting biodiversity knowledge and decision-making” to describe the impacts (including cumulative) of the expansion of offshore wind energy production on the achievement of the Good Ecological Status (GES). The request was originally submitted by DG ENV to the Knowledge Centre for Biodiversity (KCBD) via its ticketing system in December 2023, an online tool for policy Directorate-Generals to submit knowledge requests linked to biodiversity. The request received by the KCBD was handed to BioAgora to coordinate the response. Offshore wind is central to the EU’s energy transition, with targets set to increase offshore renewable generation capacity from ~16 GW today to up to 89 GW by 2030 and 366 GW by 2050. However, the expansion of Offshore Wind Farms (OWFs) must align with the EU’s environmental legislation, notably the Marine Strategy Framework Directive’s (MSFD) requirement to achieve GES across all EU marine waters by 2030 under 11 ecological descriptors. This report supports and contributes to the EU's efforts in its drive for offshore wind energy expansion. The specific aims of the report are to: ● Investigate the impacts of fixed-foundation wind turbines on each of the 11 MSFD descriptors of GES. These include biological diversity (D1), non-indigenous species (D2), commercially exploited fish and shellfish (D3), marine food webs (D4), and human-induced eutrophication (D5). They also include seafloor integrity (D6), hydrographical conditions (D7), contaminants (D8), contaminants in fish and other seafood (D9), marine litter (D10), and energy, including underwater noise (D11). ● Underscore the consequences and cumulative impacts of OWFs on marine ecosystems. ● Identify and analyse knowledge gaps through a scoping literature review and expert participatory workshop. This report combines the findings of the scoping review and a subsequent participatory workshop with external experts to assess the cumulative impacts of OWFs and knowledge gaps. The Scoping review provided a narrative synthesis of the existing evidence related to the abovementioned aims, with the findings compiled into Short Scientific Summaries (SSS) for each GES descriptor. The participatory workshop gathered expert insights and provided experimental knowledge, including key implications for OWF-associated policies, to support and complement the SSS findings.