Quattro is a permanent all wheel drive system used on Audi brand automobiles. Quattro was first introduced in 1980 on the Audi Quattro and has since been deployed to most of the models that Audi sells.

In the original quattro system, where the engine and transmission are situated in a longitudinal position, power is sent from the transmission to a mechanical center differential which splits it between the front and rear axles. After 1987, the inclusion of a Torsen (torque-sensing) center differential, instead of a manually-locking one, allowed engine power to be redirected to individual axles as driving conditions warranted. Under ideal conditions power is split 50/50 front to rear. The 50/50 split helps prevent wheel slip from starting, which is better than systems that can only react after wheel slip starts. In extreme cases, a maximum of 66-80% of the engine's power can be directed to a single axle. The power split between left and right wheels has progressed through open, lockable and eventually limited slip differentials with electronic control.

In some recent Audi models using a transverse engine and transmission positioning, power is sent primarily to the front axle and the vehicle does not use a permanent all wheel drive system. An electrohydraulic center Haldex limited slip coupler, however, may divert up to 100% of the power to the rear axle as conditions warrant. The power split between left and right wheels is achieved through limited slip differentials with electronic control. This system is also available in most Volkswagen vehicles under the name 4motion, excluding the B5 Passat which uses the above Torsen-based system.

quattro is a registered trademark of Audi AG.