A deep seismic sounding experiment was performed during the expedition ARKTIS XV/2 of the RV Polarstern and the Polish ship Eltanin in 1999 in the continent–ocean transition zone of northwestern Svalbard, along the 430-km-long profile AWI-99200. The profile runs from the Molloy Deep in the vicinity of an active spreading axis in the northern Atlantic to Nordaustlandet. Seismic energy (airgun and TNT shots) was recorded by seismic land (onshore) stations, OBSs and hydrophone systems, with airgun shots recorded up to 200 km onshore and 50 km offshore. The data recorded along the entire profile provide an excellent database for a detailed seismic modelling of the crustal P-wave velocity field along the profile track. A minimal depth of about 6 km to the Moho discontinuity was found east of the Molloy Deep. Here, the upper mantle exhibits a P-wave velocity of about 7.9 km s−1, and the crustal thickness does not exceed 4 km. The continent–ocean transition zone to the east is characterized by a complex seismic velocity structure. The Moho interface reaches a maximum depth of 28 km beneath the continental part of the profile, with a P-wave velocity in the upper mantle of 8.15 km s−1. The continental crust consists of three layers with P-wave velocities of about 5.5, 5.9–6.0 and 6.2–6.6 km s−1, respectively. In addition, we have found two reflectors in the mantle lithosphere at depths of 14–42 and 40–50 km dipping NE. The evolution of the region appears to be within a shear-rift tectonic setting. The continent–ocean transition zone is mostly dominated by extension, so the last stage of the development of this margin can be classified as rifting. The uplifted Moho boundary close to the Molloy Deep can be interpreted as the southwestern end of the Molloy Ridge.