The development of new membrane separation processes and techniques are now competing with existing industrial processes. New membrane separation techniques are receiving increasing interest from industrial sectors to enhance the separation efficiency while minimizing the energy needed. In Chapter 4, the basic principles and technologies involved in various membrane separation processes are introduced and studied. The types of membrane separation processes explained in the chapter include microfiltration, ultrafiltration, nanofiltration, high-performance tangential flow filtration, and membrane chromatography. Several types of membranes, such as plate and frame, spiral-wound and hollow-fiber membranes, are available for material separation. Plate and frame modules are relatively expensive and are used only in electrodialysis and pervaporation systems. Spiral-wound modules, which combine the principles of reverse osmosis and nanofiltration, are more economical. Hollow-fiber modules are also economical as they can pack a large membrane area in a small module size. The applications of these membranes in biotechnology, viral, and other fields are elaborated. The selection of the proper membrane material, module, and separation function is essential to obtain the most promising separation performance.