A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe.

As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport liquids.

There are many options for the motor that powers the compressor:

• Gas turbines power the axial and centrifugal flow compressors that are part of jet engines.
• Steam turbines or water turbines are possible for large compressors.
• Electric motors are cheap and quiet for static compressors. Small motors suitable for domestic electrical supplies use single-phase alternating current. Larger motors can only be used where an industrial electrical three phase alternating current supply is available.
• Diesel engines or petrol engines are suitable for portable compressors and support compressors.
• In automobiles and other types of vehicles (including piston-powered airplanes, boats, trucks, etc.), diesel or gasoline engines power output can be increased by compressing the intake air, so that more fuel can be burned per cycle. These engines can power compressors using their own crankshaft power (this setup known as a supercharger), or, use their exhaust gas to drive a turbine connected to the compressor (this setup known as a turbocharger).