It has been shown that relative projective shape, determined up to an unknown projective transformation, with respect to 5 reference points can be obtained from point-to-point correspondences of a pair of images; Affine shape up to an unknown affine transformation with respect to 4 points can be obtained from parallel projection. We show in this paper that afTine shape with respect to 4 reference points can be obtained from two perspective images provided that the pair of images is affinely calibrated. By affine calibration, it means the establishment of a special plane collineation between two image planes, this collineation is the product of two plane collineations each of which establishes a (1,1) correspondence between an image plane and the plane at infinity. Experimental results are also presented.