A general framework describing the effective electro-optic constants of an idealized free-standing superlattice, composed of thin alternating layers is derived, as a function of the dielectric and electro-optic constants of each of the N constituents. The proposed model is valid only if the energy of light is small compared to the gap of each materials. The results are applied to superlattices with layers of all classes of all symmetries (triclinic, monoclinic, orthorhombic, hexagonal, tetragonal, and cubic).