The kinetics of thermal decomposition of numerous ionic solids have been studied intensively for many years by chemists, physicists, materials scientists and chemical engineers. Many of the reactions studied form the basis of economically important industrial processes, for example, cement and ceramic production, catalyst manufacture, etc. Ln spite of all this effort, it is not possible to predict, from chemical knowledge and physical properties, what the thermal stability of a hitherto untested solid will be, or even to predict with certainty what the behaviour of a new sample of a well-tested substance will be. Some of the kinetic trends and correlations that have been identified are reviewed and possible reasons for the lack of emergence of a theory capable of predicting thermal behaviour are discussed.