The hopping process, which differs substantially from conventional transport processes in crystals, is the central process in the transport phenomena discussed in this book. Throughout the book the term hopping is defined as the inelastic tunneling transfer of an electron between two localized electronic states centered at different locations. Such processes do not occur in conventional electronic transport in solids, since localized states are not compatible with the translational symmetry of crystals.The rapid growth of interest in hopping transport has followed in the footsteps of the development of physics of disordered