The purpose of this paper is to examine the thickness of slow, intermediate, and fast shocks described by the resistive-disersive plasma model, which contains two scale lengths: the resistive length &lgr;r and the ion inertial length &lgr;i. It is found that for the case where &lgr;r≪&lgr;i, i.e., for small resistivity, slowly damped wave trains dominate the structure yielding an effective shock thickness much greater than the ion inertial length. When &lgr;r≫&lgr;i, i.e., for large resistivity, the shock structure has a thickness of the order of the resistive length so that it is again much larger than &lgr;i. Thus a minimum thickness is predicted by the resistive-dispersive model and occurs for intermediate resistivity: it is found to be a few &lgr;i for the slow shocks in distant magnetotail as well as for subcritical bow shocks and about 20 &lgr;i for intermediate shocks with typical magnetopause parameters. It is shown that the shock thickness also depends critically on the upstream plasma beta, &bgr;1=2&mgr;0p1/B12, small &bgr;1 values leading to smaller thickness. The effect of regular Newtonian viscosity on the shock thickness is also examined briefly. ¿ American Geophysical Union 1992