Silicon nitride (Si3N4) ceramic is used in numerous applications because of its superior properties, such as high-temperature strength, good oxidation resistance and low thermal expansion coefficient. In this book, the authors present current research in the study of the synthesis, properties and applications of silicon nitride. Topics include the optical and vibration properties of silicon rich nitride; high temperature oxidation of silicon nitride based ceramics; low temperature preparation of phosphate bonded silicon nitride ceramics with high mechanical strength; the SPS-sintering process and use of ceramics for high-temperature engineering applications; synthesis and properties of silicon nitride coatings; and the use of silicon nitride as biomaterial.