The upper-mantle structure of the Western Mediterranean Region, i.e. the Western Mediterranean basins with the surrounding land areas, has been investigated by means of surface-wave analysis. Phase velocities of teleseismic Rayleigh waves have been obtained from the records of a specially designed long-period seismic station network. The dispersion data have been regionalized employing a computerized procedure and have then been inverted by means of the so-called “hedgehog” method. The upper mantle shows pronounced lateral heterogeneities which are correlated with the tectonic activity of the region. Some deep anomalous features are revealed such as the “soft” continent-like structure of the lithosphere under the Alboran Sea, the absence of lithospheric roots below the mountain range of the High Atlas, the continental platform-like upper mantle along the northern margin of Africa. While the upper mantle under the Provençal and the Algerian basins shows oceanic or back-arc basin-like structure, the Balearic Promontory and particularly the Valencia Trough are shown to possess upper mantle structure with characteristics close to those of a continental rift system. We therefore suggest that the boundary—at the level of the upper mantle—between the African and the European plates, should rather be viewed as a broad transition zone involving the upper mantle of the entire Western Mediterranean region across which the plate interaction takes place.