The authors describe the theoretical work and practical results obtained in recent years in the area of separation of powders in moving flows. The promising nature of the cascade separation method is stressed. Mathematical models of regular, combined and irregular cascades are described. Mathematical fundamentals of the structural, dynamic and kinetics models of the process are presented. A new approach to optimising the separation processes, based on the separation curves and information theory, is explained. Experience with the industrial application of cascade classifiers is presented. The book is suitable for scientists and engineering working on various aspects of powder technology and ore enrichment. It may also be used as a textbook for university and college students in the area of mining, engineering chemistry, metallurgy, energetics, constructional engineering, etc.