A general but simple model is described to account for charge transport which is applicable not only to insulating polymers but also to those that have been doped to higher levels of conductivity. Charge transport is considered to occur by tunnelling transitions between localized states where the reorganization energy is an essential part of the localization. Expressions are obtained for the transient, a.c. and d.c. conductivities which, in their temperature and time and frequency dependences, are in agreement with experimental results for a number of polymers. An important feature is that these dependences can be used to determine the energy distribution of the localized transport states. It is concluded that these states correspond to the Urbach states at the optical absorption band edge of the polymer. The doping role of metal electrodes is also discussed.