This report is a contribution to the Strategic Environmental Assessment (SEA4) conducted by the Department of Trade and Industry (now Department of Energy and Climate Change). It is a synthesis of information describing the seabed habitats, species and communities on the continental shelf of the west of Orkney and Shetland relevant to the SEA 4 area. It provides a summary of the benthic communities and assemblages which inhabit the shallow waters of the SEA4 area, from littoral to offshore areas. A wide range of habitats exist in the area because of the heterogeneity of the seafloor environment, ranging from hard rock sites exposed to the full force of waves and tidal currents to muddy sediments in sheltered inlets. The shelf and offshore areas include varying bedforms of sand and gravel, some of high carbonate content, and considerable amounts of glacigenic material. The epifauna and infauna which inhabit these different environments are summarised. A section of the report discusses the environmental impacts of anthropogenic activities in the area. These include the harvesting of algae from rocky shores, the release of radionuclides on the Caithness coast (Dounreay), dredging for sedimentary material, trawling and mariculture, in addition to the offshore oil and gas industry.