The Cape Smith Belt is one of the most interesting and controversial of the proposed geosutures in the Canadian Shield. A new tectonic model is presented in which the mafic–ultramafic thrust sheets of the belt constitute a klippe, 20 000 km2 in area, separated from underlying basement of Superior Province and its thin autochthonous cover by a continuous décollement exposed along the north margin and the plunging eastern end of the belt. Thrusting is directed southward, and the entire stack is folded into a regional antiform (north of the belt) and synform (the belt itself). It is proposed that the décollement is rooted 30–90 km north of the belt, in a zone paralleling Sugluk Inlet, across which there is a major positive deflection in the Bouguer gravity field, an abrupt switch from broad north–south to narrow east–west magnetic anomalies, and a change in metamorphic grade from amphibolite to granulite facies from south to north. In the model, this zone is a north-dipping ductile shear zone juxtaposing crusts of two collided continents. Accordingly, granulite north of the zone represents lower crust of the overriding plate, whereas granulite between the zone and the klippe occurs in antiformal culminations in the underriding plate. One test of the model is that the south-dipping shear zone observed at the north margin of the belt should have a normal sense of slip. Another is that north-dipping banded gneiss at Sugluk Inlet should mark a ductile shear zone, also having a south-directed sense of overthrusting. A structural profile of the belt and its relation to basement can best be worked out by down-plunge projection of the eastern end of the belt.