Britain has some of the finest, most extensive and fossilferous exposures of marine Lower Jurassic rocks seen anywhere in the world. They include remarkably complete stratigraphical successions and a great diversity of facies, forming the basis for many detailed investigations. Knowledge accrued at many of these sites has contributed enormously to enhancing our understanding of the factors that influenced these Early Jurassic sediments, such as relative sea level, basin subsidence, climate and diagenesis. The British Lower Jurassic strata have also long been famed for its wealth of fossils, both vertebrate and invertebrate, with a great many species having been first described from Britain. Rich ammonite faunas at many sites have formed the basis for one of the highest resolution biostratigraphies of any part of the geological column. Numerous palaeontological case studies have also contributed immensely to our understanding of the biological diversity of the early Jurassic and of evolutionary patterns and processes, marine palaeoevironments, and the processes of fossilization during this time interval. Described here are 45 sites, from small disused quarries to magnificent coastal cliffs, which represent the entire British outcrop, from North-East Scotland to South Wales and South-West England. Together they demonstrate the diversity of Lower Jurassic stratigraphy and facies in Britain. All are of considerable importance within a British and Western European context, while some unquestionably are of international significance.