As an alternative to the conventional water treatment processes, membrane technologies were developed in early 1960s. A membrane is a thin layer of semipermeable material that separates substances when a driving force is applied across the membrane. Membrane processes are increasingly used for removal of bacteria, microorganisms, particulates, and natural organic material. Membrane filtration has shown great potential in water treatment in terms of its superior-treated water quality. This chapter provides information on principles and mechanics of filtration and different types of membrane filtration and shows the way forward to using membrane-based technologies as modular design alternatives for flexibility in design. © 2022 Elsevier Inc. All rights reserved.