  We present a unified view of the transport properties of small-polarons in
the Holstein model at low carrier densities, based on the Dynamical Mean Field
Theory. The nonperturbative nature of the approach allows us to study the
crossover from classical activated motion at high temperatures to coherent
motion at low temperatures. Large quantitative discrepancies from the standard
polaronic formulae are found. The scaling properties of the resistivity are
analysed, and a simple interpolation formula is proposed in the nonadiabatic
regime.
