The Mercedes-Benz W 21 was a six-cylinder passenger car launched in 1933 using the name Mercedes-Benz Typ 200. It was one of several Mercedes-Benz models known, in its own time, as the Mercedes-Benz 200 (or sometimes, in this case, as the Mercedes-Benz Typ(e) 200) and is therefore in retrospect more commonly referred to using its Mercedes-Benz works number, “W21”

The side-valve six-cylinder engine had a capacity of 1,961 cc which produced a claimed maximum output of 40 PS (29 kW; 39 hp) at 3,200 rpm. The engine shared its 85 mm (3.3 in) piston stroke length with the smaller 6-cylinder unit fitted in the manufacturer's W15 model, but for the W21 the bore was increased by 5 mm (0.20 in) to 70 mm (2.8 in). The stated top speed was 98 km/h (61 mph) for the standard length and 95 km/h (59 mph) for the long bodied cars. Power passed to the rear wheels through a four-speed manual transmission in which the top gear was effectively an overdrive ratio. The top two ratios featured synchromesh. The brakes operated on all four wheels via a hydraulic linkage.

During the model's final year, Mercedes-Benz announced, in June 1936, the option of a more powerful 2,229 cc 55 PS (40 kW; 54 hp) engine, which was seen as a necessary response to criticism of the car's leisurely performance in long bodied form.