Abstract The Moine Supergroup (Fig. 9) can be defined as follows: ‘A succession of metasedimentary rocks that unconformably overlies the Lewisian Complex which is tectonically bounded to the west by the Moine Thrust and to the southeast by the Great Glen Fault’. Previous definitions have included certain rocks found SE of the Great Glen in the Moine (e.g. Johnstone 1975; Harris & Pitcher 1975) but some or all of these are probably better referred to the Grampian Group of the Dalradian for reasons set out in Chapter 4. Many of the Grampian Group rocks resemble Moine units lithologically, but there is no conclusive proof of their lithostratigraphical equivalence. Furthermore, as no rocks that can be proved to be Dalradian occur north of the Great Glen Fault, the exact age relationship between Moine and Dalradian supergroups is uncertain. Units of the Moine Supergroup as defined here probably do not occur in Ireland because the Great Glen Fault lies offshore and to the north (e.g. Klemperer et al. 1991). Lithologies very similar to the Moine are found in Shetland, notably on the island of Yell (Flinn 1985).