The great potential of microelectrode measurements in several fields of solid state ionics is discussed and exemplified: (i) Microelectrodes are perfectly suited to investigate inhomogeneous bulk conductivities in ionic solids. This is demonstrated for a SrTiO3 single crystals with a non-stoichiometry profile. (ii) Microelectrode experiments are helpful in determining the distribution of grain boundary properties in ceramics with highly resistive grain boundaries. Data obtained on a SrTiO3 polycrystal are shown as an example. (iii) Experiments with microelectrodes allow the detection and quantification of highly conductive grain boundaries; the applicability of this measurement mode is demonstrated for AgCl. (iv) Microelectrodes can serve as model electrodes with well-defined three phase boundaries and interfaces. Investigations on Sr-doped LaMnO3 microelectrodes, for example, yielded an improved understanding of electrochemical processes in solid oxide fuel cells. (v) Microelectrodes are very sensitive to highly conductive surface layers and therefore suited to investigate ionic materials with enhanced surface conductivity (e.g. AgCl). (vi) Several other applications of microelectrodes in solid state ionics are briefly touched upon. (C) 2003 Elsevier B.V. All rights reserved.