A simple model is presented for the coupled dynamics of the orbit-rotation-climate system of Mars. Changes in the orientation of the spin pole, relative to the orbit pole, influence the spatiotemporal pattern of incident radiation and thus drive climatic mass transport into and out of the polar regions on a variety of timescales. Changes in the mass distribution occur from direct climatic forcing and compensating viscous flow in the interior. The net change in mass distribution influences the rate of spin axis precession and thereby influences obliquity. The rate of secular obliquity drift depends on several poorly known parameters, including the magnitudes and response times of volatile inventories and viscosity structure within Mars. Even relatively modest secular obliquity drift can lead to trapping in nearby resonances. The dissipative nature of the coupled dynamical system makes reconstruction of past evolution much more difficult than for a purely inertial system. The long-term obliquity history of Mars is dominated by climate. ¿ 1999 American Geophysical Union