The new materials design was established for the structural ceramics to break through the present monolithic and composite ceramics. In this concept, the ceramic-based composites were divided into two groups: micro and nanocomposite. The microcomposite is the so-called composite in which the micro-sized particles, whiskers, platelets and fibers are dispersed at the grain boundaries of matrix grains. The nanocomposites, on the other hand, have three types of structures: intra and intergranular nanocomposites and nano/nano composite. The intra and intergranular nanocomposites were found to show the tremendous improvement of mechanical properties even at elevated temperatures compared with those of monolithic and microcomposite ceramics. The nano/nano composites gave the new functions such as machinability and superplasticity like metals. Our final goal for developing supertough and strong ceramics was achieved by hybridizing the intra and intergranular nanocomposites with the micro-meter sized fibers. This new concept was found to be also applicable for ceramic-metal composite systems.