Deep seismic profiling and gravity data show that the continental crust under the Valencia trough has been thinned by up to a factor of three in the centre, and that the uppermost mantle there has an unusually low density. Structural mapping in the borders of the Valencia trough shows important asymmetry, and there are asymmetrical features in the geophysical modelling. There are many aspects of the basin formation that are still to be worked out.