In this paper, we describe the generally adopted process of fabrication and propose a criterion for the optimal design of side mirrors and rear-view mirrors. This criterion is that the root-mean-square of the difference between the two principle curvatures on the mirrors shall be minimum. Finally, we propose a new design for the shape of a mirror with a wide viewing angle. It is a non-spherical mirror and, in order to reduce the image distortion, the variation of the curvature along the curve on its surface is a constant. We also point out how to produce this mirror in practice.