Existing sediment and sedimentary rock nomenclature has been based on composition, texture and other physical attributes as well as depositional environment, genetic relationships and local economic importance. A consistent, workable classification for all sediments and sedimentary rocks needs a set of unifying boundary conditions: this classification attempts to do this. The sediment and sedimentary rock names used are descriptive and it should be possible to classify and name any sediment or sedimentary rock without knowledge of its field setting and without making assumptions about its mode of origin. There are sections on siliciclastics, carbonates, dolomites, phosphates, iron sediments and ironstones, organic rich sediments and rocks, non-carbonate salts, non-clastic siliceous sediments and sedimentary rocks, miscellaneous hydroxides and oxides, sediments and rocks based on grain size, hybrid sediments or sedimentary rocks, volcaniclastics and qualifiers. The report, issued here as BGS Research Report RR 99-03, includes 14 figures and 12 tables.