The Tornquist Zone is a fundamental structural lineation representing the southwestern margin of the East European/Fennoscandian Precambrian basement platform. It is characterised by complex, often rejuvenated, dip-slip and strike-slip faulting and frequently by tectonic inversion. The zone extends across Poland, beneath the southern Baltic into Skåne and northem Denmark. Evidence obtained from offshore oil and gas exploration suggests that the Tornquist Zone extends beneath the southern Norwegian North Sea at least as far as the line of the Viking Graben, some 500 km beyond its commonly assumed termination at the line of the Oslo Graben.