The sea surface topography, which is directly linked to the shape of the geoid and to oceanic effects, is only measurable thanks to the spatial and temporal resolution of satellite altimetry. The contributions of Seasat (1978), Geosat (1985) followed by ERS-1 (1991) and TOPEX/Poseidon (T/P) (1992) to the study of the Mediterranean have been considerable. The first maps of the marine geoid, with relative accuracy of 10-20cm depending on the methods used, have contributed greatly to the understanding of geophysical phenomena. Subsequently, thanks to reductions in orbital errors, improvements in gravitational models, and to the development of pseudo-geometrical orbit computations, the accuracy of determination of the absolute mean sea level has improved from several metres to a few centimetres. The analysis of T/P data in the Mediterranean presented here has allowed seasonal variations in mean sea level to be determined for the first time. Amplitudes are of the order of 20cm with a maximum in October/November and a minimum in March. Further, the combination of ERS-1 and T/P data has permitted improvements in the spatial resolution of sea surface maps without loss of accuracy, thereby showing the main features of Mediterrenean circulation including seasonal variations.