The Audi RS 4 quattro is the top tier and highest performing version of some specific generations of the Audi A4range of automobiles. It is a sports-focused compact executive car (often called sport compact in some countries), produced by Audi's high-performance private subsidiary quattro GmbH, in limited numbers, for German car manufacturer AUDI AG, part of the larger Volkswagen Group. It slots distinctly above the Audi S4, as the fastest, most sports-focused model based on the A4's "B" automobile platform. The RS 4 made a comeback in 2012, in Avant form only based on the Audi A4 Avant.

The original B5 version was produced only as a five-door five-seat "Avant", Audi's name for an estate car/station wagon. The second version, the B7, was released initially as a four-door five-seat saloon/sedan, with the Avant following a short while later. A two-door four-seat Cabriolet version was subsequently added. Furthermore, their unique internal combustion engines are all front-mounted, and are longitudinally oriented. The transmission is mounted immediately at the rear of the engine in a longitudinal orientation, in the form of a transaxle, and contains both a center and front differential.

The "RS" initials are taken from the German: RennSport—literally translated as "racing sport", and is the Audi marque's highest trim level, positioned above the "S" model specification of Audi's regular model line-up. Like allAudi "RS" cars, the RS 4 pioneers some of Audi's latest advanced technology, and could therefore be described as a "halo vehicle". Furthermore, it is only available with Audi's Torsen-based "trademark" quattro permanent four-wheel drive system.

Its main market competitors include the BMW M3, Mercedes-Benz C63 AMG, Lexus IS-F and Cadillac CTS-V .