The potential impact of high densities of interfaces in nanocrystalline solids on ionic conduction and defect formation are examined. The Literature on three oxides; cubic zirconia, ceria and titania, is reviewed. While it remains too early to make firm conclusions, the following observations are made. Additives which contribute to ion blocking at grain boundaries are diluted in nanocrystalline oxides giving rise to substantial reductions in specific grain boundary resistivities. The case for enhanced ionic conduction in nanocrystalline oxides remains unresolved due to conflicting reports and inadequate efforts to isolate the ionic from the total conductivity. There is strong support for the notion that the energetics for defect formation may be substantially reduced in nanocrystalline oxides leading to markedly increased levels of nonstoichiometry and electronic carrier generation.