This report contains the results of 15 days diving (May-September 1983) between the East Solent and Selsey Bill. Observations from previous years are also included. The underwater geology of this area has been studied extensively by Wallace. Recently members of the Oceanography Department, Southampton University (Hall 1982) have worked with Wallace to further map bottom features in order to determine the coastline structure following recent glaciations. The seabed has been studied remotely by echosounding, side scan sonar and seismic profiling. Decca navigation has been used for this work and the study described here. Linked to this has been a diving programme to examine interesting features. The authors have been involved with the geological studies since 1981. An abundance of life on the various features compared to the surrounding sand and gravel seabed was noted, hence this study. Published information on the marine life of the study area is limited. The review of the Solent Estuarine System (NERC 1980), covering most fields of study, extends into the north-west corner of the region. The marine life off the Sussex coast east of Selsey Bill has been studied by members of the South-East Underwater Conservation Society (SEUCS 1983). Studies of the alien alga Sargassum muticum and associated species by workers at the Portsmouth Polytechnic Marine Laboratory, Hayling Island, include the East Solent and Bembridge (Knight-Jones et al, 1975; Gray, 1978; Critchley, 1981). Chamberlain (1977) has studied coralline red algae on the Isle of Wight including Bembridge. The description of the role of seaward in shingle transport by Joliffe and Wallace (1973) covers both sides of Selsey Bill. There is much archaeological evidence that the original northern shore of the area extended from Horse Tail, south of the Medmery Bank to the Mixon (Longcroft, 1856). Wallace concludes that in the 13th century, the sea broke through and rapidly established the existing shoreline. Roman Selsey and Church Rocks, Hayling Bay have been described by McKee and Wallace (McDonald, 1968). Working in collaboration with geologists, a number of seabed features, identified from side-scan sonar and echo sounder surveys, have been examined. The bottom is mainly sand and gravel. Limestone outcrops to the west and south of Selsey Bill and also to the east of Bembridge are present. Ridges of clay bedrock are found to the south and east of Chichester Harbour entrance. There are many mounds of cobbles and boulders, e.g. Bullock Patch, north and west Medmery Bank and New Grounds which are probably glacial moraines. An interesting feature of the area is the widely scattered rectangular limestone sarcens up to 5 m across. Light penetration is generally poor due to the presence of fine muddy silts from the East Solent and harbours to the north as well as the clay outcrops. Underwater photography was used extensively to aid identification of species and define habitats. The principal habitats described are sand, gravel, cobble, boulder, clay bedrock and limestone bedrock. There is a clear increase in species diversity and abundance with substrate particle size. Shallow limestone outcrops have the richest flora and fauna. Any stable surface from gravel upwards is normally covered with an extensive growth of ascidians, hydroids and bryozoans. Visually dominant species at many sites below 8 m were Dendrodoa grossularia, Nemertesia antennina, Tubularia indivisa, Flustra foliacea and Alcyonidium gelatinosum. Smaller hydroid and bryozoan species (e.g. Halecium halecinum, Obelia spp, Bugula turbinata, Epistomia bursaria) contribute to a thick turf on prominant surfaces. Tube dwelling worms are common, Sabellaria sp. on most surfaces and Lanice conchilega in sand and gravel. Algal growth is limited over much of the area due to depth. However, the shallow limestone reefs support a rich flora. Exposed clay and limestone outcrops are extensively bored by the bivalves, Pholas dactylus and Barnea sp. respectively. Large beds of Crepidula fornicata are found in the approaches to the East Solent and, to a lesser extent, Mytilus edulis south of Selsey Bill. Gravel extraction and fishing are the main commercial uses of the area. Sewage disposal and hydrocarbon exploration are noted.The area is important for recreation, principally sailing and angling. Scientific and archaeological interest is reviewed. Recommendations for further work are made, including reefs, algae and boulder habitats. Records currently considered sensitive have been removed from this dataset.