This book is all about the membrane separation process, where a brief approach had been followed to explore the maximum of membrane. The reader must understand that the book is divided into two segments as a whole. The first chapter says about the basics of membrane to give the reader an introductory glimpse of membrane to understand and analyze the membrane applications. The subsequent chapters enlighten the applications of membrane at different scale from wastewater process to biomedical applications. Chapter 3 says the membrane application in bioprocess engineering, where the reader is expected to meet the applications of membrane in the production of biobutanol, a complete replacement of gasoline. While the subsequent chapter, i.e. chapter 4 says the biomedical application of membrane. This chapter elaborates the dialysis process and the application of membrane in gas exchange with the extracorporeal membrane oxygenator (ECMO) device. In case with the wastewater process, the book further discusses the application of membrane and the membrane reactor. In the second part, i.e. from chapter 6 onwards a discussion is made on the numerical of membrane applications. The reader can divide the numerical applications discussed here in two parts - one, the deterministic and the second one is the stochastic. Chapter 6 discusses the basics of numerical techniques to solve the mathematical model on membrane process. Chapter 7 says the basic mass balance model for the membrane process, while chapter 8 and 9 discuss the stochastic approach to model the membrane process. The chapters elaborate the applicability and the relevance of the stochastic model for the membrane process. I feel the reader the book paves a pathway for the reader to extend their ideas on membrane separation process from its application to its instrumentation.