Two detailed seismic refraction lines were shot in northern Baffin Bay in order to determine the crustal structure and so provide constraints on the complex geological and tectonic history of the area. An array of air guns provided the seismic source, with a total of 16 ocean bottom seismometers as receivers. The data were analyzed by iterative forward modeling of travel times and arrival amplitudes, and the crustal velocity structure obtained was interpreted in the light of previous seismic reflection and refraction results from this area, together with other available geological and geophysical information. Plate reconstructions suggest that the region was a single entity from the Archean until the late Mesozoic, when it underwent successive stages of extension, translation, and compression. On line 2, at 76¿ N, the continental crust thins between Greenland and Ellesmere Island, reaching to a minimum of about 10 km beneath a narrow, linear basin, which may delineate a former transform plate boundary. On line 4, on the northern margin of Baffin Bay, there is a marked change in velocity structure across the apparent continent-ocean boundary, with continental crust being replaced by a layer of intermediate seismic velocity that is believed to be serpentinized mantle, indicating that northern Baffin Bay was formed by amagmatic continental rifting and separation. A thick sedimentary sequence is the result of erosion of the Eurekan Orogen to the north, which was formed during the final, compressional tectonic motion. The seismic refraction results are consistent with the tectonic history inferred from plate kinematics.¿ 1997 American Geophysical Union