This report introduces a lithostratigraphical framework to formation level for the Early Jurassic, predominantly argillaceous, succession of England and Wales, traditionally known as the Lias. The outcrop has been divided into four depositional areas - the Cleveland Basin, the East Midlands Shelf, the Worcester Basin (plus the adjoining Bristol-Radstock Shelf) and the Wessex Basin. The approach adopted, however is one of unification, emphasising similarities between areas rather than differences and retaining well established names where possible. Full specifications are given for the 12 formations (Beacon Limestone, Blea Wyke Sandstone, Blue Lias, Bridport Sand, Charmouth Mudstone, Cleveland Ironstone, Dyrham, Marlstone Rock, Redcar Mudstone, Scunthorpe Mudstone, Staithes Sandstone and Whitby Mudstone) and for the Lias Group, which they comprise. The report is illustrated by three figures and four tables and also contains appendices listing formations with BGS Lexicon codes, formations with preferred BGS map symbol and redundant names and codes. It is released here as BGS Research Report RR 99-01.