We show, using the concept of the polarization potential tensor &bgr; which relates energy band shifts to the crystal polarization, that the nonlinear optical (NLO) tensor coefficients &dgr; in oxygen‐octahedra ferroelectrics are proportional to the quantity &bgr;PswherePsis the crystal spontaneous polarization. Because &bgr; is found to be nearly the same in all oxygen‐octahedra ferroelectrics, we are able to calculate the &dgr; coefficients from a knowledge ofPs. The polarization‐induced energy band shifts are shown to be nearly the same for static polarizations (giving rise to the clamped electro‐optic effect) and for optical‐frequency electronic polarizations (giving rise to nonlinear optical effects).