An improved model of Martian global topography has been obtained by fitting a sixteenth-degree harmonic series to occulation, radar, spectral, and photogrammetric measurements. The existing observations have been supplemented in areas without data by empirical elevation estimates based on photographic data. The mean radius is 3389.92¿0.04 km. The corresponding mean density is 3.9331¿0.0018 g cm-3. The center of figure is displaced from the center of mass by 2.50¿0.07 km toward 62¿¿3¿S, 272¿¿3¿W. The geometric flattening (fg= (6.12¿0.04) ¿10-3) is too great and the dynamic flattening (fd= (5.22¿0.03) ¿10-3) is too small for Mars to be homogeneous and hydrostatic. It is confirmed that the low-degree gravity harmonics are produced primarily by surface height variations and only secondarily by lateral density variations. Maps of the data distribution, global topography, and Bouguer gravity anomaly are presented. These are interpreted in terms of a crustal thickness map which is consistent with gravity, topography, and recent preliminary Viking seismic results. From plausible density contrasts and an assumed zero crustal thickness at Hellas, the inferred minimum mean crustal thickness is 28¿4 km.