The primary function of the intake manifold is to evenly distribute the combustion mixture (air and fuel) to each intake port in the cylinder head. Proportionate distribution is important to optimize the efficiency and performance of the engine.

The intake manifold may also serve as a mount for the carburetor, throttle body, fuel injectors and other components of the engine.

Because of the downward movement of the pistons and the restriction caused by the throttle valve, a partial vacuum pressure exists in the intake manifold. This manifold vacuum can be used as a source of ancillary power to drive auxiliary systems such as ignition advance, power assisted brakes, cruise control, windshield wipers, power windows, ventilation system valves, etc.

This vacuum can also be used to draw any piston blow-by gases from the engine's crankcase. This is known as a closed crankcase ventilation or positive crankcase ventilation (PCV) system. This way the gases are burned with the fuel/air mixture.

Intake manifolds have historically been manufactured from cast aluminum or cast iron. However, composite plastic materials are gaining popularity and have been used in most newer Chrysler 4 cylinder engines, Ford's Zetec 2.0, Duratec 2.0 and 2.3 engines, and GM's Ecotec series engines.