Automobiles were one of the most important forces in twentieth century America. Beginning in the 1920s, the automobile industry became the backbone of a consumer goods society, providing one out of six American jobs. By 1982, automobile manufacturing accounted for more than a third of the economy, and was the primary customer for steel and petroleum. In a few short decades, the automobile industry revolutionized many industries.

Motorcycles began as self-propelled bicycles in the late nineteenth century. This innovation was the answer to the 19th century dream of a self-propelled carriage. In 1884, Edward Butler developed the first commercial three-wheeler, which featured a horizontal single-cylinder gasoline engine with steerable front wheels and a drive chain to the rear wheel.

Motorcycles are auto-propelled vehicles, although they only carry one or two passengers. Some motorcycles may also have sidecars. Motorcycles are not considered automobiles in some courts, although there are cases where they have been ruled to be non-automobiles. The distinction between an automobile and a motorcycle is based on the way a vehicle is used, and how many passengers it can carry.

The automobile revolution changed the face of the United States. It is one of the most popular means of transportation, both for business and pleasure. Automobiles are among the most valuable types of Personal Property in the U.S. and are often highly taxed. They are also the targets of thieves and contribute significantly to air pollution. Furthermore, they can cause tremendous personal injury. Automobile law covers four broad stages in the automobile life cycle: