Significant progress has been made in recent years in developing silicon nitride ceramics. The advances that have been achieved are mainly based on an increasing understanding of processing and microstructure-properties relationships. New analytical methods and high resolution transmission electron microscopy (HRTEM) coupled with extensive phase equilibria studies have provided new insights into the grain boundary region and offer the possibility to tailor the microstructure for specific applications. Because of the anticipated break-through in industrial applications there are still...