Ferroelectric thin films are of considerable promise for use as electro-optic, and non-linear optical materials. Electro-optic (EO) waveguide devices fabricated from thin films offer several advantages over bulk material including lower driving voltages, smaller size, higher modulation speeds and the potential for monolithic integration. Recently we reported ferroelectric thin film electro-optic modulators that operate at frequencies up to 20 GHz. We have also investigated the dynamic response of the electro-optic effect in thin film BaTiO@sub 3@ and KNbO@sub 3@ . The dynamic response has a temporal dependence given by the expression t@super -m@exp(-Bt)@super n@. Measurements of the film birefringence, polarization and dielectric transients show qualitative agreement over 11 orders of magnitude in time. The observed dependence is attributed to the dynamic response of ferroelectric domains.