The Theory of Recycle Processes in Chemical Engineering deals with the theory and methods related to dynamic (flow) systems and with the processes in static systems with recycles, The book investigates complex recycle processes through the use of concepts and examples. The development and refinement of chemical technology involves processes that are purely chemical or technological in nature. The technological approach consists in the design of industrial processes where chemical reaction occurs with minimum by-products, and with the maximum useful employment of each unit of catalyst surface and reaction space. The book explores effective systems for the complex processing of chemical raw materials using the technological approach. The text reviews the elementary principles of the theory of recycle process through derivation of equations for simple recycling processes where one or more chemical reactions occur in a single medium or reactor in which the reactions happen consecutively, or in a parallel manner. The book also explains how the investigator can determine the technologically-optimum characteristics of the reaction unit employing five steps. The text will benefit industrial chemists, researchers, technical designers, and engineers, whose works are related with chemistry and recycling.