Valve timing is a mechanism using valves to control the flow of working gases (air, fuel, exhaust gases) through a piston combustion engine. This is the most common type of mechanical distribution, used mainly in four-stroke internal combustion engines.

The opening of the valves is controlled by the respective cam of the camshaft, which is driven by the crankshaft. In four-stroke engines, the camshaft rotates 2x slower than the crankshaft, because one working cycle of the engine takes two revolutions of the crankshaft.