Many ceramics are commonly used in solid electrolyte devices. Micro- and nano-structural features, apart from intrinsic behaviour, play a critical role in defining their electrical and mechanical properties. An overview of the effect of powder and ceramic processing techniques on the micro- or nano-structures and phase assemblage has been given for different types of ceramics with main emphasis on zirconia-based materials. The effect of micro- and nano-structural features both within the grains and across grain boundaries on both the electrical and mechanical properties has been discussed along with nano-phase processing of ceramics and the actual micro- or nano-structural features in the sintered ceramics. The effect of grain size and grain boundary phases on superplastic deformation and degradation of tetragonal zirconia in moist environments has been considered.