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The Great Glen Fault (GGF) is a major northeast to southwest trending structure and has been interpreted as a terrane boundary separating the Precambrian Moine terrane to the northwest from the Precambrian Dalradian terrane to the southeast (e. g. Bluck & Dempster 1991). If the GGF is a terrane boundary no `Moine' rocks could be found southeast of the GGF and no `Dalradian' rocks could be found to the northwest of the GGF and each crustal block would have distinct tectonometamorphic, provenance and igneous intrusive characteristics. To assess this, carefully selected orthoamphibolite and metasediment samples were collected from both the Northern and Central Highlands, and were analysed by a combination of petrography, geochemistry and geochronology. Geochemical analysis suggests that a Neoproterozoic metagabbro and metadolerite suite was emplaced during crustal extension across the Northern and Central Highlands at approximately the same time, and that this suite represents an earlier intrusive event to that represented by amphibolites in the Dalradian Appin Group. Geochemistry also suggests that the Upper Morar Psammite Formation of the Moine Supergroup in the Northern Highlands is unlikely to correlate with the pebbly psammite formations in the Central Highlands and shows that the Upper Shiaba Psammite Formation metasediments on the Isle of Mull are geochemically distinct from the Upper Morar Psammite Formation metasediments on the mainland. The Glen Urquhart Complex in the Northern Highlands cannot be correlated with the Ord Ban Subgroup or Grantown Formation in the Central Highlands. However, despite these differences U-Pb detrital geochronology shows that the Upper Morar Psammite and Central Highland pebbly psammite formations are dominantly derived from similar Mesoproterozoic and Palaeoproterozoic sources, with a small amount of material of Archaean derivation. This, together with the matching amphibolite suites, means that the Great Glen Fault is very unlikely to be a terrane boundary.