Muscle cars are high-performance automobiles made primarily in Detroit from 1964 to 1974. Car manufacturers placed large V8 engines in mid-sized cars, giving them quite startling performance and setting off intense competition between manufacturers to produce the most powerful and extreme machine. The 1973 OPEC oil embargo, stricter air pollution laws and insurance premiums killed most muscle car models, though they are actively collected and restored.

Although auto makers such as Chrysler had occasionally experimented with placing a high performance V-8 in a lighter mid-size platform, and full-size cars such as the Ford Galaxie and Chevrolet Impala had high-performance models, Pontiac usually gets credit for starting the muscle car trend with its Pontiac GTO, based on the rather more pedestrian Pontiac Tempest. Spearheaded by Pontiac division president John De Lorean, the GTO proved far more popular than expected, and inspired a host of imitations and a general trend towards performance, both in the true 'muscle car' class of intermediate vehicles, and also the smaller pony cars like the Ford Mustang, Plymouth Barracuda and AMC AMX, and more luxurious and expensive vehicles such as the Buick Riviera.

However, a large part of the appeal behind muscle cars was that they were mostly inexpensive models young drivers could afford. For instance, Chevrolet placed an extremely large 396 cubic inch (6.5 Liter) engine in its compact Nova. In today's terms this would be equivalent to attempting to make a Chevy Prizm with a Corvette motor (though the performance gains would be vastly different in such a project today as smaller, modern engines can use newer technology to produce vastly more power than their same-sized counterparts from the muscle car era). Mopar also had several low-cost models, such as the Dodge Super Bee and Plymouth Road Runner.

Between 1964 and 1970, Detroit auto makers were in competition for the bragging rights to the most powerful motor. Power numbers generally hit their peak in 1970; the Chevelle SS 454 from that year is generally considered to have had the highest advertised output, producing 450 horsepower (336 kW) from a 454 cubic inch (7.4 Liter) engine. By 1971, muscle cars began to fall out of favor and disappear, with one of the last muscle car holdouts being Pontiac's Trans Am 1973 and 1974 SD455 model (while the SD455 was considered the last muscle car, the Trans Am nameplate continued until 2002).

While fast (sometimes extremely fast) in a straight line, most had primitive brakes and suspension (compared with modern vehicles and also European sports cars of the time), and tires which were inadequate to handle the acceleration and speeds the engines made capable. These inadequacies have all been to some degree addressed by after-market suppliers, of course.

A pony car is a class of automobile. The term is applied to North American-built "baby muscle cars"—performance cars built on compact (by American standards) passenger car chassis. The first cars of this type appeared as 1965 models in mid 1964 as the Ford Mustang (after which the type is named) and Plymouth Barracuda. Subsequent pony cars included the Chevrolet Camaro, Pontiac Firebird, Mercury Cougar, AMC Javelin and Dodge Challenger. The second of the three Mercury Capri models also qualifies.

Of these, only the Ford Mustang is still in production, although the Camaro and Firebird were built until 2002.

Pony cars were designed to be more affordable than their larger muscle car brethren, and were substantially smaller and lighter. Earlier versions often could not accommodate the manufacturer's largest, most powerful engines for that reason, although all were later modified to correct this.

Some high-performance models were rated as fairly capable performers in their day, and had some racing success. They were always sporting conversions of regular passenger cars, though, in terms of chassis design, rather than dedicated sports cars, and like muscle cars were generally better in a straight line than when agile handling was required, although this could be addressed to some degree with aftermarket upgrades.

Old pony cars are nowadays highly collectable, especially the high-performance models.