The ignition in an engine is a collective term for the various components which are involved in timing, producing and transmitting the requisite 'spark' into an internal combustion engine which ignites the fuel/air mixture inside the engine's cylinders. Modern versions, involving electronic switches rather than purely mechanical systems, are known as electronic ignition. Note that Diesel engines, which rely on compression heating to ignite their fuel/air mix, do not have an ignition system!

The term is also loosely used at times to refer to the starter system (starter motor, ignition switch) which is technically incorrect, but in wide use.

In rocketry, ignition is used to refer to the moment that a rocket motor or engine reaches self-sustaining combustion. For boosters, this will typically occur just before lift-off.