BMW E21 is the body designation for the first BMW 3 Series compact executive car, produced by the German automaker BMW from 1975 to 1983. This series was the immediate successor to the BMW 2002 and was superseded by the BMW E30.

Under the direction of its 51% percent shareholder, Herbert Quandt, BMW decided upon a replacement for their aging 2002. Without it, there was the distinct possibility of BMW leaving its core mission of building driver oriented cars, and alienating an existing customer base long enamored with the company's 2002 model.

Paul Bracq, Director of Design at BMW from 1970 to 1974, is credited with setting the design direction of the E21 3 Series, while Wilhelm Hofmeister is credited with first drawing the small forward wedge at the base of the C-pillar, a strong design trait of the first 3 Series. In 1975 Claus Luthe replaced Bracq and became the owner of the project.

In July 1975, BMW’s Board of Management first presented this new model series in the Munich Olympic Stadium for public appraisal. The frontal view of the new car was dominated by the BMW trademark kidney grille standing out clearly from the radiator cover. The styling of the new car bore a resemblance to the BMW E12 5 Series.

The BMW 3 Series is a compact executive car manufactured by the German automaker BMW since May 1975. Successor to the BMW New Class, it has been produced in six different generations and in no fewer than five different body styles. It is BMW's best-selling model, accounting for around 30% of the BMW brand's annual total sales (excluding motorbikes).

BMW released its E21 in the wake of the 1973 oil crisis, attracting customers seeking both prestige and economy, nearly doubling BMW's worldwide auto sales figures in three years, and winning numerous automotive world awards and honours. The 3 series has also maintained BMW's racing heritage. The M version of the 3 series, M3, debuted in 1988.

There have been six generations of the 3 Series, and their respective chassis codes:

The two-door saloon model only. A factory authorised cabrio version was also built by Baur. The series was superseded by the BMW E30 series.

The cockpit design of the E21 marked the introduction of a new design concept for BMW, with the center console angled towards the driver. This feature has become part of BMW’s interior design philosophy for many years. As a sign of passive safety, all edges and control elements within the interior were rounded off and padded.