We have mapped the deep structure of the Slave craton by combining analysis the effective elastic thickness (Te) with data on mantle samples from numerous kimberlites. Three-dimensional mapping of the subcontinental lithospheric mantle (SCLM), using mantle-derived xenoliths and xenocrysts in kimberlites, has shown that much of the craton is underlain by a strongly layered SCLM; a highly depleted upper layer (low in basaltic components Ca, Al, Fe) is separated from a relatively fertile lower layer by a sharp boundary. This boundary lies at 140--150 km depth in the Lac de Gras area and shallows to ≤100 km in the northern and southern parts of the Craton. Weak lithosphere (Te 56 km), in the younger eastern part of the craton, is separated from the older western part by a zone of steep Te gradient parallel to the major locus of kimberlite intrusion, which may map the deep extension of the boundary between the two domains. Another strong Te gradient across the Kilohigok Basin accompanies a marked compositional change in the upper layer of the lithospheric mantle; the Basin probably marks a major translithospheric fault. Correlations between Te and mantle composition suggest that Te is strongly influenced by the rheology of the upper mantle.