This book presents the theoretical background to the behaviour of fluidised beds in a form suitable for teachers and students of chemical engineering and for designers of process plant. It is important because it approaches the subject from first principles of fluid mechanics to problems of a truly chemical engineering nature. At all stages the theoretical treatment is directly related to experiment. Such a synthesis, much of which is based on recent research work by the authors and others, should also help to guide designers in the scaling-up of experimental work on small apparatus to pilot and production plant.