A timing belt or cam belt (informal usage), is part of an internal combustion engine that controls the timing of the engine's valves. Some engines, such as the flat-4 Volkswagen air cooled engine, and the straight 6 toyta f engine use timing gears. Timing belts replaced the older style timing chains that were common until the 1970s and 1980s (although in the last decade there has been reemergence of chain use for many carmakers). Some manufacturers, such as BMW and Mercedes Benz are known for utilizing timing chains, because of their durability. The term "timing belt" is sometimes used for the more general case of any flat belt with integral teeth, although such usage is a misnomer since there is no timing or synchronization involved.

When the vechicles timing belt is replaced, care must be taken to ensure that the valve and piston movements are correctly synchronized. Failure to synchronize correctly can lead to problems with valve timing, and this in turn, in extremes, can cause collision between valves and pistons in interference engines such as Vauxhalls Vectras, Audi A4 and most other vehicle. It is vital that the timing belts are replaced just before the manufacures recommends to replave the belts as if the timing belt fails it will cost a lot of money.