The discovery of sialons in 1971 was a significant step in the history of nitrogen ceramics, because it broadened the field into a wider range of chemistry, and simultaneously increased the flexibility to modify microstructure and properties. During the last 35 years this has resulted in the development of a spectrum of materials, mainly based on the α- and β- structural forms. However, the subject has remained broadly within the scope of structural ceramics. During the 1990s, a range of new sialon derivatives were prepared with a more varied starting chemistry, and the corresponding final materials demonstrated a correspondingly wider variety of structural complexities. In response, many sialon researchers have started to broaden their interests beyond the limiting horizon of structural applications, and considerable progress has been made in the development of transparent and coloured materials, and also derivatives with useful electronic properties.This enlargement of the sialons field is still in its infancy, but promises to generate a much wider spectrum of materials, which can be tailored to meet the increasingly multifunctional requirements of modern day engineering applications.