Grain Size Control reviews significant developments in the understanding of solid state grain size control over the past half century to provide an advanced text for materials science students and practitioners. Fifty years ago, Zener had already formulated his relationship of the inhibiting influence of fine particles on grain growth. The derivation of the Zener relationship is presented here, together with the refinements that have been introduced as a result of our increased understanding of granular arrays and the importance of irregularities in such arrays. The important effects of particle size and volume fraction are illustrated with applications drawn from the author's experiences with ferrous materials. The importance of particle solubility and of Ostwald ripening is emphasised, as any inadequacy in volume fraction and particle size can lead to abnormal grain growth. Consideration is also given to the grain growth inhibiting effect of thermally etched grooves operating in thin strip foils, when free surface energy effects become more important than grain boundary energy. Exercises, accompanied by worked examples at the end of the book, are given at the end of relevant chapters to enable the reader to calculate particle requirements and how these are attained in practice.