Plymouth was a marque of automobile based in the United States, marketed by the Chrysler Corporation and DaimlerChrysler from 1928 to 2001.

The Plymouth automobile was introduced on July 7, 1928. It was the Chrysler Corporation's first entry in the low-priced field, which at the time was dominated by Chevrolet and Ford. Plymouths were actually priced a little higher than the competition, but they offered standard features such as hydraulic brakes that the competition did not provide. Plymouths were originally sold exclusively through Chrysler dealerships.

The origins of the first Plymouth can be traced back to the Maxwell automobile. When Walter Chrysler took over control of the trouble-ridden Maxwell-Chalmers car company in the early 1920s, he inherited the Maxwell as part of the package. After he used the company's facilities to help create and launch the Chrysler car in 1924, he decided to create a lower-priced companion car. So for 1926 the Maxwell was reworked and rebadged as a low-end Chrysler model. Then at the end of the decade this model was once again reworked and rebadged, this time to create the Plymouth.

While the original purpose of the Plymouth was simply to cover a lower-end marketing niche, during the Great Depression of the 1930s the car would help significantly in insuring the survival of the Chrysler Corporation in a decade when many other car companies failed. Beginning in 1930, Plymouths were sold by all three Chrysler divisions (Chrysler, DeSoto, and Dodge). Plymouth sales were a bright spot during this dismal automotive period, and by 1931 Plymouth rose to the number three spot among all cars.For much of its life, Plymouth was one of the top selling American automobile brands, along with Chevrolet and Ford ("the low-priced three"). Plymouth even surpassed Ford for a time in the 1940s as the second most popular make of automobiles in the U.S. Through 1956, Plymouth vehicles were known for their durability, affordability and engineering. In 1957, Chrysler's Forward Look styling theme produced cars with much more advanced styling than Chevrolet or Ford, although Plymouth's reputation would ultimately suffer as the cars were prone to rust and sloppy assembly. The marque also introduced its limited production Fury line in 1956, and it too benefited from the crisp Forward Look designs.

The Plymouth brand lost market share rapidly in the early 1960s. While Plymouth was a styling leader from 1957 to 1958, its 1959 through 1962 models were awkwardly styled cars that failed to strike a chord with the public. Plymouth also found itself in competition with its own corporate sister division Dodge when the lower-priced, full-size Dodge Dart was introduced for 1960. Rambler, and then Pontiac would assume the number three sales position for the remainder of the decade. Plymouth went into a decline from which it would never fully recover.

The marque regained market share following the introduction of the 1965 models, which returned Plymouth to full-size vehicles and more mainstream styling. Plymouth regained its traditional third place in the sales race in 1971 and 1974, primarily with its popular Valiant and Duster compact models, but as a brand Plymouth was hardest hit by Chrysler's financial woes of the late 1970s. Marketing decisions ultimately reduced the Plymouth lineup to the point that it was no longer a full-line make (by the late 1990s, only four cars were sold under the Plymouth marque: the Voyager/Grand Voyager minivan, the Breeze mid-size sedan, the Neon compact car, and the Prowler sports car). New models were increasingly given to the Dodge and Chrysler brands, but denied to Plymouth. By 1979, its lineup consisted of only the domestically produced Volare and Horizon models, and a number of rebadged Mitsubishi imports.

After discontinuing the Eagle brand in 1998, Chrysler was planning to expand the Plymouth line with a number of unique models before the corporation's merger with Daimler-Benz AG. The first model was the Plymouth Prowler, a modern-day hot rod. The PT Cruiser was to have been the second. Both models had a similar grille, showing that Chrysler was intending to take a retro styling route with the Plymouth brand. Other than the Prowler, at the time of the takeover Plymouth had no unique products that were not also available in the Dodge line. Furthermore, whereas all Plymouth dealers also sold the Chrysler line of cars, many Dodge dealers sold only Dodge; thus it would cause much more dealer disarray to discontinue Dodge than it would to discontinue Plymouth. Consequently, DaimlerChrysler decided to drop the make after a limited run of 2001 models. The last new model sold under the Plymouth marque was the second generation Neon for 2000-2001. The PT Cruiser was ultimately launched as a Chrysler, and the Prowler and Voyager were absorbed into that make as well. The Plymouth Breeze was given new life as the Chrysler Sebring sedan. Most Plymouths had twins from either Dodge, Chrysler, Eagle, or Mitsubishi.