<p>Processing of superplastic metal-matrix composites by the friction stir processing (FSP) was reviewed in this monograph. It was summarized that by increasing the deformation temperature, it is possible to attain the maximum superplastic elongation at higher strain rate, facilitating the occurrence of high strain rate superplasticity (HSRS). However, the thermal stability of the matrix against grain coarsening was found to be an important prerequisite, which can be improved by incorporating the reinforcing particles. Moreover, the effects of the reinforcement content on the grain refinement, HSRS, and particle distribution were also critically discussed. Furthermore, useful suggestions for future works were proposed, including focusing on the common matrices and innovative reinforcing phases such as high-entropy alloys, grain refinement by dynamic recrystallization (DRX) and its evaluation similar to hot deformation studies, metal additive manufacturing processes, and low temperature superplastic forming.</p>