A vacuum pump is an instrument that is used to remove gas molecules from a sealed volume so that it may leave behind a partial vacuum. It was invented by Otto von Guericke in 1650 and has been used for inventions by other famous scientists, so as Nikola Tesla. They are used for a number of different applications.

There are three broad categories that vacuum pumps can be placed into. The first one is positive displacement, in which the pump uses a mechanism to expand a cavity by process of repetition, allowing the gas to flow from its chamber, seal off the cavity, and displace it to the atmosphere. They are the most effective for low vacuums and is used in the case of fluids, which cannot have a vacuum created by suction but must be done by creating an artificial vacuum first, either by increasing the volume or another technique, before using suction to create the permanent vacuum.

The second type of vacuum pump, a momentum transfer pump or molecular pump, uses high speed jets of dense fluid in order to knock the gaseous molecules from the chamber. Some instances prefer a high speed rotating blade to create the vacuum. This type of vacuum pump is often used in conjunction with one or two positive displacement pumps. This creates the most common configuration that is used to achieve high vacuums. In momentum transfer specifically, gas molecules are accelerated from the vacuum to the exhaust, which is only possible at a pressure below 1 kPa.

The third type of vacuum pump is called an entrapment pump. Entrapment pumps are used for the purpose of capturing gases in their solid or absorbed state in order to then use these forms for other purposes. These could include cryopumps, which condense gas using cold temperatures, or ionization pumps, that access strong electrical fields in order to ionize gases and propel these ions into a substrate. Other examples include sorption pumps and getters.