A new model of the rotation of Mars is presented. It is designed to support the analysis of radio metric data from the Viking landers and possible future Mars-lander missions. The precession and nutation are represented by series that include all terms causing a maximum Mars surface displacement of at least 1 cm after 10 years. The precession rate is estimated from Mars physical constants to be (7.58\¿0.03\) yr-1 based on Reasenberg's (1977) model of the mass distribution of Mars. We also discuss some geophysical effects that may cause Mars surface displacements larger than the 1-cm criterion.