The Mercedes-Benz W126 is the company’s internal designation for its second generation S-Class, manufactured in sedan/saloon (1979–1991) and coupé (1981–1990) models, succeeding the company’s W116 range. Mercedes introduced the 2-door C126 coupé model, marketed as the SEC, in September 1981. This generation was the first S-Class to have separate chassis codes for standard and long wheelbases (W126 and V126) and for coupé (C126).

The long 12-year production (1979–1991) resulted in 818,063 sedans/saloons and 74,060 coupés being built, totalling 892,123. W126 is so far the most successful and the longest in production for S-Class.