The Audi A4 is a line of compact executive cars produced since late 1994 by the German car manufacturer Audi, a subsidiary of the Volkswagen Group.

The A4 has been built in four generations and is based on Volkswagen's B platform. The first generation A4 succeeded the Audi 80. The automaker's internal numbering treats the A4 as a continuation of the Audi 80 lineage, with the initial A4 designated as the B5-series, followed by the B6, B7, and the current B8. The B8 A4 is built on the Volkswagen Group MLB platform shared with many other Audi models and potentially one Porsche model within Volkswagen Group.

The Audi A4 automobile layout consists of a longitudinally oriented engine at the front, with transaxle-typetransmissions mounted at the rear of the engine. The cars are front-wheel drive, or on some models, "quattro" all-wheel drive.

The A4 is available as a saloon/sedan and estate/wagon. The second (B6) and third generations (B7) of the A4 also had a convertible version, but the B8 version of the convertible became a variant of the Audi A5 instead as Audi got back into the compact executive coupé segment.

Facelift (1997–2001)

A refreshed B5 A4 range appeared at the 1997 Frankfurt Motor Show, with sales beginning in Europe in early 1998. The 2.8 litre 30-valve V6 engine replaced the 2.8 litre 12-valve. A 2.5 litre V6 Turbocharged Direct Injection (TDI) diesel engine with 150 PS (110 kW; 148 bhp) was standard on the quattro. A six-speed manual gearbox was available, as well as the new high-performance Audi S4, now part of the A4 lineup (the previous S4 had been an Audi 100). Cosmetic updates included new rear lights, headlights, door handles, and other minor exterior/interior changes.

In mid-1998, the 1.8 20vT engine available outside Europe had its power output raised to 170 PS (125 kW; 168 bhp). The previous KKK K03 turbocharger, although fundamentally unchanged, received revisions on the turbine side to prevent cracking due to heat. The 12-valve V6 was replaced by the 30-valve unit which had been available in Europe for two years.

A further facelift took place across the A4 and S4 platform in February 1999 as a 1999.5 model; changes were largely cosmetic, but affected many components, such as both front and rear bumpers, the front and rear lights, the center console, and door handles.

In 1999 Audi also debuted an even higher performance RennSport model, the RS4 Avant, like its predecessor RS2, available only in the Avant bodystyle.