A method for determining the relative motion between an antenna and a target using SAR data is presented. The motion is broken into two parts: translation and rotation. The translation is relative range motion between the antenna and a point fixed with respect to the target. The rotation is defined by an axis of rotation vector with origin at the point and target rotation about the vector. The net result is that four functions of time completely describe the motion, one for translation and three for rotation. For an isolated scatterer the negative of the phase (in cycles) is twice the range to the scatterer divided by the radar wavelength. For real scenes the phase is corrupted by neighboring scatterers and so provides only approximate information about the motion functions. The procedure is to locate strong scatterers, obtain maximum likelihood estimates of the motion from the phase, adjust the pulses according to the motion, and repeat until convergence is achieved. Arbitrary translational motion can be found in this way. However, even with a rigid target assumption, general rotational motion can not be found. The rotation must be restricted in some way. An example where the rotation is restricted to rotation about a fixed axis is included.