A naturally-aspirated engine or normally-aspirated engine refers to an internal combustion engine (normally petrol or diesel powered) that is neither turbocharged nor supercharged.

Most automobile gasoline (petrol) engines are naturally-aspirated, though turbochargers and superchargers have enjoyed periods of success, particularly in the late 1980s and the current 2000s era. However, most road-going diesel-engined vehicles use turbochargers, because naturally-aspirated diesels generally cannot offer suitable power-to-weight ratios to be acceptable in the modern car market. For petrol engines the two main types of engine are the common piston engine or the rotor wankle engine.