Seismic refraction and magnetic data from the continental margins of Labrador and south Greenland are interpreted in relation to knowledge of onshore geology.Two high-velocity seismic layers are measured on the inner part of the continental shelf off northeast Labrador. These are tentatively correlated with Precambrian crystalline rock onshore. There is no evidence that Paleozoic rock is present offshore. No obvious expression of the Grenville front is seen in the seismic results.Two sediment layers of variable thickness overlie the two high-velocity layers, and have accumulated to as much as 2 km total thickness in some localities.The crustal structure of the Labrador basin is interpreted to extend beneath the outer part of the Labrador shelf. No evidence is found from the seismic refraction measurements for fault-control of the marginal channels on the Labrador shelf. Where observed, they appear to be erosional in nature.Considerable relief is present in the high-velocity basement rock beneath the south Greenland slope. It appears to outcrop halfway down the slope.