At the third meeting of the DETR Working Group on the Review of Marine Nature Conservation, on 27 January 2000, English Nature, the other country agencies and JNCC were charged with developing a more detailed view on the criteria and marine biodiversity to be included within any future possible national-level framework and advising on the timetable necessary to achieve this. This was to be undertaken for Great Britain, with Northern Ireland and the Republic being brought in later as appropriate. 1.2 This paper is provided in fulfilment of that action. It should be noted, however, that in the time available it has not been possible to place equal emphasis on seascapes (including seabed geology and earth science interests), on habitats and on species (including seabirds and fish). The paper is accordingly biassed towards near-shore benthic habitats and benthic species, although the principles and criteria established in this paper are unlikely to significantly change when addressing the other remaining aspects of the marine environment.