This book mainly provides a comprehensive treatment of the SiBCN ceramics and their matrix CMCs, aspect of theme content including material design and preparation, microstructural feature and evolutionary process, mechanical and thermophysical properties, resistance to oxidation, thermal shock and ablation, and the mechanisms of oxidation, ablation and crystallization of SiBCN-based materials. Furthermore, this book offers the necessary fundamentals to ensure a basic understanding of the structure and properties of metastable Si-based ceramics and their composites for undergraduate and postgraduate students in materials-related disciplines in higher education, as well as for scientific research, production development and technical management in the fields of metastable materials, mechanical alloying processing nonequilibrium structure, organic-inorganic composites, etc.