The origin of this book can be traced to a Workshop held at the University of Cambridge in December 1985 under the auspices of the Wolfson Group for Studies of Fluid Flow and Mixing in Industrial Processes. This Group was es tablished at the University of Cambridge in January 1983 and includes mem bers from the Departments of Applied Mathematics and Theoretical Physics, Engineering and Chemical Engineering. As its name suggests, the objective of the Group is to undertake, coordinate and stimulate research in various aspects of fluid flow and mixing in industrial processes. However, another equally important aim for the Group is to promote co-operation between the University and industry at all levels from collaborative research projects to joint colloquia. The Workshop in December 1985 on 'Mixing, Stirring and Solidification in Metallurgical Processes' which led to this book was one in an annual series of such meetings first held in December 1983. The existence of the Wolfson Group is due to the enthusiasm of its original advocate, the late Professor J. A. Shercliff FRS, Head of the Department of Engineering who, together with Professor G. K. Batchelor FRS, Professor J. F. Davidson FRS, Dr J. C. R. Hunt, and Dr R. E. Britter, were responsible for the initial application to the Wolfson Foundation and for the subsequent direction of the Group's activities.