Reflection profiles offshore of Baffin Island, south of Lancaster Sound, reveal coast-parallel half-grabens containing flat-lying sedimentary sections typical of a rifted margin. In northernmost Baffin Bay, adjacent to Devon and southern Ellesmere islands, four sedimentary basins are identified. In these basins the sedimentary sections are faulted, folded, and laterally discontinuous. The basement shows linear trends, steep faults, and abrupt variations in depth. In one basin a 50 km long and 10 km wide "flower structure" is observed. A transpressive tectonic regime is suggested to explain the uplifted sedimentary and basement section and the change in depth to basement across it. A 150 km long paleoshelf, buried by a thickening sedimentary wedge, is present offshore of Devon Island. Because strike-slip and compressional features are observed on seismic profiles north of Lancaster Sound and extensional features are observed to the south, differences in the plate tectonic development are inferred. The interpretations of the seismic reflection records are shown to be compatible with plate motions determined by matching magnetic anomalies in the North Atlantic, the Labrador Sea, the Norwegian and Greenland seas, and the Eurasia Basin. In addition, the onshore geology of Baffin Island, Labrador, and Greenland is consistent with the predrift position of the plates.