An electrically dimmable rear-view mirror for motor vehicles of simple and robust construction, suitable for use as an outside mirror or as an interior mirror possessing a transmission layer which is composed of a PLZT ceramic, on which a linear birefringence can be imposed by means of a controlling electric field. The transmission layer is located between a linear polarizer and a reflective layer, the latter being designed as a dielectric multilayer arrangement. Suitable comb-type electrodes are located on that side of the reflective layer which faces away from the transmission layer and, if appropriate, on that side of the polarizer which faces the transmission layer, the function of these comb-type electrodes being to generate the controlling field. The polarizer defines the direction of polarization, which is inclined at 45.degree. with respect to the field direction and/or the optical axis of the transmission layer. The strength of the electric field controlling the dimming effect is regulated in a manner such that the effective reflectivity of the rear-view mirror is reduced to suit the prevailing situation, this field-strength regulation being accomplished by a photoelectric control system which reacts, on the one hand, to the brightness of the surroundings and, on the other hand, to the intensity of a luminous flux passing through the polarizer and the transmission layer.