This review discusses the processes at electrodes and grain boundaries, the applications of electrodes, and the characterization of electrodes and grain boundaries. The electrode processes considered are charge transfer and diffusion limitation. The applications of electrodes are presented for both current-carrying contacts and voltage probes. The nature of grain boundaries and the asymmetry in their conductivity for currents flowing parallel and perpendicular to the boundary are discussed. Experimental methods for characterization of electrodes and grain boundaries, mainly electrochemical ones, are reviewed.