This competitor of BMW 3 Series and Mercedes C Class was introduced in 1994 and is based on VW's MLB platform. Though initially it couldn't compete with performance and looks of 3 Series, or even C Class for that matter, but tides of time started shifting in Audi's favor from 2001 when B6, or second generation, A4 was unveiled. A4 still maintained its distinctive Audi looks but styling, finish and performance were on another level, ever since 2001 Audi is incorporating similar sporty design in all of its vehicles. Completely redesigned exterior and interior made A4 an instant success. From a compact executive car struggling with mediocre makes, A4 instantly entered the elite group and was compared favorably with icons like BMW and Mercedes.
The second generation A4 garnered massive support from press and media mainly because of its V6s, both in diesel and petrol. 2.5 litre Audi A4 diesel engine was one of the most talked about diesel engine, it was capable of producing 178 bhp whereas the equivalent 2.4 litre petrol engine produced 168 bhp. B7 or third generation A4 incorporated similar design features and continued with sports theme. Audi increased more engine variants both in petrol and diesel category to better capture the market in compact executive sedan category. This time around Audi included three turbo charged, 1.8 litre (20v), 1.8 litre (16v) and2.0 litre (16v) petrol engines, whereas whole diesel lineup was based on TDI technology.
Traditionally Audi A4 is a front wheel drive car, gearbox at the rear, in third generation Audi introduced "Quattro" or AWD models as well, to better compete with rear wheel drive BMW 3 Series and Mercedes C Class. Inclusion of AWD became an instant hit as now the biggest Audi A4 diesel engine, 3.0 litre V6 with 233 bhp, could cover 0-60 miles in less than 7 seconds, whereas the biggest petrol engine, 3.6 litre V6 with 256 bhp, managed same feat in under 6.4 seconds.
Previously A4 was mainly competing on looks, as of third generation it started competing with BMW and Mercedes on performance grounds as well. This generation continued from 2006 till 2008. B8, fourth and current generation of A4, produced from 2008 onwards, is designed on similar notes as Audi's R8, with almost identical daylight LEDs. Fourth generation A4 became a top seller in US instantly, because of sportier styling and similar high performing petrol and diesel engines.