Mott [Philos. Mag. 19, 835 (1969)] established the single-phonon variable range hopping conduction from occupied to unoccupied localized states in disordered materials at low temperatures by assuming a constant localized density of states at the Fermi level. However, recent researches have reported that this behavior can also be observed in the polycrystalline films with an exponential tail state distribution in the gap. If the carrier concentration is lower than a critical value for a semiconductor-to-metal transition, in a low temperature region polycrystalline films exhibit percolation hopping through band tail states with an exponential distribution. We revisit various hopping conductions for inorganic semiconducting polycrystalline films. (c) 2006 American Institute of Physics.