Ireland’s Marine Strategy Framework Directive (MSFD) assessment area is subdivided into ecologically meaningful spatial units known as Marine Reporting Units (MRUs). These units serve as the basis for evaluating indicators and conducting integrated assessments of marine environmental features, tailored to specific MSFD descriptors. A total of 24 MRUs have been delineated, encompassing Ireland’s full MSFD area, including the 12 nautical mile Territorial Sea limit, merged Water Framework Directive (WFD) coastal waterbodies, and national components of regionally defined assessment units under OSPAR. These include areas relevant to descriptors such as contaminants, sea-floor integrity, food webs, and offshore eutrophication, as well as designated shellfish waters. The MRU framework ensures spatial consistency and ecological relevance in national and regional marine environmental reporting.