Chemical engineering process synthesis has been an important subject in the chemical engineering field. The aim of this subject is to find a flowsheet of processing units in order to convert feed material into chemical products. Superstructure optimization is a valuable tool to formulate a mathematical programming model which embeds an optimal solution of a chemical engineering process synthesis problem. This book gives a review about major trends of superstructure optimization in the chemical engineering process synthesis. Discussion about different models in the literature are presented to give the reader fundamental understanding of superstructure optimization. Then, hybrid membrane networks for wastewater treatment are discussed as applications of superstructure optimization. A generic representation is provided to give the reader tools for the hybrid membrane superstructure construction. Beside, different solution algorithms and applications are given as examples for the hybrid membrane systems.