In membrane filtration, a solute is passed through a semi-permeable membrane. The membrane's permeability is determined by the size of the pores in the membrane, and it will act as a barrier to particles which are larger than the pores, while the rest of the solute can pass freely through the membrane. The result is a cleaned and filtered fluid on one side of the membrane, with the contaminated solute on the other side.

Nanofiltration, ultrafiltration, microfiltration, and reverse osmosis are all membrane filtration techniques. In all cases, the size of the pores has to be carefully calculated to exclude undesirable particles, and the size of the membrane has to be designed for optimal operating efficiency. Membranes are also prone to clogging as the pores slowly fill with trapped particles, which means that the system must provide accommodations for easy cleaning and maintenance so that it can be kept in good working order.

Many membrane filtration systems are designed for industrial uses. One of the big advantages to such a system is that it does not require the use of chemicals or additives, which cuts down on operating costs. Additionally, membrane filtration requires minimal energy, and it can in fact be designed to run on almost no energy, with a pressurized system which takes advantage of gravity and forces the solute through the membrane at a steady rate.

Successive membrane filtration, in which the solute passes through a series of membranes, is very popular. In this approach, the pores get progressively smaller, removing more and more impurities from the fluid. This technique reduces clogging of the system as the solute is slowly filtered, and it carries the added advantage of fitting into a compact space, because the membranes can all be very small and still work efficiently.Waste management, industrial food handling, medicine, and laboratory science all have uses for membrane filtration systems. These systems are generally easy to use, although they must be maintained properly in order to be effective.