A longitudinal engine is an engine mounted in a vehicle so that the engine's crankshaft is parallel with the vehicle, front to back. The majority of rear wheel drive vehicles use a longitudinal engine design. where the engine's crankshaft axis is parallel to the vehicle. Many modern front wheel drive vehicles use a transverse engine mounting design.

Engines may be placed in three main positions within the car:

• front engine mounted - the engine is mounted under the hood, over the front axle
• rear engine mounted - the engine is mounted where the trunk would normally be, over the rear axle
• mid engine mounted - the engine is mounted between the front and rear axles, where the rear seats would be located