The Mercedes-Benz S-Class is a series of the largest sedans produced by Mercedes-Benz, a division of Daimler AG. The S-Class, a product of nine lines of Mercedes-Benz models dating since the mid-1950s, is the world's best-selling luxury flagship sedan. As the foremost model in the Mercedes-Benz lineup, the S-Class has debuted many of the company's latest innovations, including drivetrain technologies, interior features, and safety systems (such as the first airbag supplemental restraint systems, seatbelt pretensioners, and electronic stability program). The latest generation, the W221 S-Class, premiered in 2006 as an all-new design. As in previous iterations, the latest S-Class is sold in standard and long wheelbase versions and offers V6, V8, V12, and diesel powertrains.

The name "S-Class" derives from the German word "Sonderklasse" of which "S-Class" is an abbreviation. Sonderklasse means "special class" (or rather: "In a class of its own"), and in automotive terms thus refers to "a specially outfitted car." Although used colloquially for decades, the "S-Class" designation was first officially applied in 1973 with the debut of the W116 model line. Since then, five generations of officially-named S-Class sedans have been produced. Past two-door coupe models of the S-Class became known as the CL-Class in 1998.

In early Mercedes-Benz history, the "S-Class" designation was used colloquially, referring to the letter "S" which designated most of the larger six-cylinder powered vehicles in the company's lineup (but not the luxurious V8-powered 600 limousine).

In some early cases, as in the "Ponton" model, the "S" was applied to vehicles requiring premium fuel ("Super" in Germany) due to the higher compression ratio and output of the company's top-of-the-line engines. These six-cylinder engines were available in the W180/128 chassis lines, Mercedes' first without a conventional frame, using a unitized body/frame construction. This line was introduced in the mid-to-late 1950s, and came to encompass the 220a, 219 (W105), 220S, and 220SE (sedan, coupe, and convertible) models. Both "Ponton" models were produced through the 1950s.

In 1959, the "Ponton" body was replaced by the new 220Sb with "Einheitskarosserie" (standard body) with "Fintails", with the different six-cylinder "S"-versions of the W111 mainly differing from the smaller 4-cylinder variant W110 by a different length of the front, and the amount of chrome applied. Thus, the W110, introduced in 1961 as a predecessor to the modern E-Class, featured a shorter hood for the "economy" models 190c and 190Dc. The W112, as 300 SEL with a longer wheelbase, was for the short period the top model of Mercedes, succeeding the baroque "Großer Mercedes" ("Grand Mercedes") 300, 300b, 300c, and 300d, which were often associated with chancellor Konrad Adenauer. In 1965, the W111 line also added the 230S sedan.