Magnetic, gravity, and seismic sub–bottom profiles are used to contribute to the structural interpretation of the Greenland Sea and environs. The most anomalous feature of the magnetic survey is the subdued magnetic expression of the Mid–Atlantic Ridge north of the Jan Mayen fracture zone. Over the median rift valley magnetic anomalies are an order of magnitude smaller than those recorded in the Atlantic Ocean. A suggested explanation, supported by seismic data, is that crustal tension decreases northward along the ridge. The inferred structural consequence is that the tensional mid-oceanic ridge merges into the compressional Verkhoyansk Range beneath the Arctic Ocean. Gravity data suggest an abrupt increase in crustal thickness under the Greenland continental shelf. Maximum seismic penetration into the sediments of the ocean floor was 1.2 sec. Due to masking by strong bottom reflection multiples, poor sub–bottom resolution was obtained on the continental shelf. The steep and jagged continental slope off Kronprins Christian Land, the occurrence of seamounts, and the proximity of earthquake epicenters support the thesis that the Lena Trough is the medial rift of a northern extension of the Mid–Atlantic Ridge. The sub–bottom profile oft the east coast of Greenland reveals three widely separated faults. These correlate with projections of known tectonic features and suggest: (1) The thrust fault of the main Caledonian orogeny of northeastern Greenland extends to a depth in excess of 3 km and continues into the ocean floor at least 85 km from the coast; (2) the Jan Mayen fracture zone, which offsets the Mid–Atlantic Ridge, extends into Greenland at approximately 72° N.; and (3) the Caledonian fold belt may correlate directly between eastern Greenland and northern Britain.