In this paper, we review our systematic grain-boundary studies ofzirconia ceramics using bicrystals. Yttria-stabilized cubic zirconia (YSZ) bicrystals with  symmetric tilt grain boundaries are systematically fabricated by diffusion bonding method. It is revealed that the grain-boundary atomistic structures are strongly dependent on the macroscopic geometries of the boundaries. High-resolution transmission electron microscopy (HRTEM) combined with lattice statics calculations suggest that the grain-boundary structures are characterized by the accumulation of coordination deficient cation sites at their cores, whose densities have a clear correlation with their excess energies and amounts of yttrium solute segregation. The orientation dependence of grain-boundary properties in cubic zirconia can be thus linked and understood via local grain-boundary atomistic structures with the characteristic miscoordinated cation sites. These unique sites will be used to discuss the differences in energies and solute segregation behaviors with fee metal grain boundaries.