We have interpreted all available single-channel and multichannel seismic reflection profiles to produce maps of structure contours on basement and isopachs of sediment thickness in the northwestern Atlantic Ocean, including the Labrador and Irminger basins. Where appropriate, we have modified and incorporated existing charts into the compilation. Contours are in meters, derived by applying velocity-regression equations based on sonobuoy results; this gives a more accurate representation of geologic relations than is possible in reflection-time mapping. Major structural relations and sediment distribution for the Mid-Atlantic Ridge, Mid-Labrador Sea Ridge, Davis Strait, and adjacent Greenland and eastern Canadian continental margins are clearly defined in the maps. Observed basement structure is in good agreement with that expected from current plate-kinematic models of the region. The sedimentthickness patterns are controlled by interaction of such factors as age of underlying oceanic crust, crustal tectonic history, structural trends in basement, locations of sediment sources, and nature of the sedimentary processes deUvering sediment to the basins.