The time of maximum switching currenttmof triglycine sulfate (TGS) crystals has been measured as a function of fieldEand crystal thicknessdin the ranges 102<E<103V/cm and 0.02<d<0.98 cm. The results may be expressed astm=t∞exp[&agr;0d−⅔/E] witht∞≃(1.3±0.3)×10−4sec and &agr;0=(4±1)×102V/cm. The symmetry of the switching transients abouttmis a function ofdand increases slightly withE.The symmetry factormvaries fromm=0.7 tom=0.4 for 0.5<d<1.0 cm in agreement with a model for polarization reversal in which the virtual sidewise displacement of domain walls is the dominant mechanism. For thin crystals,d<0.15 cm andm<0.1, a model based on dominant nucleation and growth of antiparallel domains is consistent with experimental observations.