This paper describes a method for autocalibrating a stereo rig. A planar object perfforming several general and unknown motions is observes by the stereo rig and, based on point correspondences only, the autocalibration of the stereo rig is computed. a stratified approach is used and the autocalibration is computed by estimating first the epipolar geometry of the rig, then the plane at infinity (affine calibration) and finally the absolute conic (Euclidean calibration). We show that the affine and Euclidean calibrations involve quadratic constraints and we describe an algorithm to solve them based on conic intersection. Experiments with both synthetic and real data are used to evaluate the performance of the method.