Membrane processes are key unit operations in almost all parts of the chemical, biochemical, and pharmaceutical downstream processing. In this book, microfiltration, ultrafiltration, nanofiltration, and reverse osmosis will be introduced. Flux, trans-membrane pressure, osmotic pressure, osmotic pressure model, resistance towards mass transport, concentration polarization, gel layer model, and membrane fouling are all important terms that will be explained and described - all in an easy understandable way with many illustrations and examples on a bachelor or master of science level.