This talk will review recent research on using three and four phases to create nanocrystalline and sub-micron grain size materials that maintain a stable fine grain size at high temperatures. Grain growth in these multiphase ceramics is sluggish as long-distance, coordinated diffusion of ions across the surface of interfaces between dissimilar phases is required, while grain growth due to the rapid transport and reorientation of atoms across grain boundaries between the same phase is limited. Four phase ceramics should provide the optimal case with no grain boundaries existing between similar phases in three dimensions for perfect mixing. One challenge is that the final phases must be thermodynamically stable with respect to each other and have minimal liquid phase formation. Approaches using reactive phase sintering, electric field assisted sintering, and compression sintering, as well as conventional sintering will be discussed for optical and thermal applications and superplastic forming using multiphase ceramics.