Origin of high ionic conduction in superionic conductors is understood from the double minimum potential produced from strong third and fourth order terms of the phonon displacements. Such terms are derived from low energy and low dispersion of the optical and acoustic phonon modes that originate from enhanced electronic polarization of superionic conductors. Based on the double minimum potential, we attempt to explain why dielectric parameters correlate closely with the ionic activation energy and transition temperature, and describe the effects of the low energy phonon mode, large phonon damping, and the heavy atomic mass of the frame ion on the high ionic conduction. (C) 2004 Elsevier B.V. All rights reserved.