Automobiles (also called motor vehicles or motor cars) are wheeled passenger vehicles that typically run primarily on roads and are constructed principally for the transportation of people. Most modern automobiles use an internal combustion engine to drive their wheels. An engine usually burns a liquid fuel such as gasoline or diesel fuel to produce power which is transmitted to the vehicle’s wheels by a drivetrain. The term automobile is often used to refer to the entire motor vehicle, including the chassis and bodywork, but can also be applied to individual parts such as the engine, transmission, and control systems.

The automobile revolutionized American industry and daily life in the first half of the twentieth century. It ranked as the most valuable industrial product, and it was the backbone of a new consumer-oriented society. It accounted for one out of every six jobs in the United States and drove many other industries, including steel and petroleum. It provided a massive market for ancillary products, such as rubber and plastics, and created new businesses like gas stations and convenience stores.

In the early years of the twentieth century, Henry Ford brought automobiles within the reach of middle-class Americans by inventing modern mass production techniques. His Highland Park, Michigan, plant built Model T runabouts at a cost of $575 in 1912, less than the average annual wage then in force. The Ford company soon became the largest automobile manufacturer in the world. By the 1920s it was followed by General Motors and Chrysler.

Having an automobile opens up opportunities for work, family life and social involvement. It enables people to live in the most desirable areas of a city or region without having to rely on expensive public transport. It permits people to travel longer distances to work and leisure activities, to include many more relatives in their social circle, and to find better housing with more space to expand.

However, the automobile has some negative effects on the environment and human health. It contributes to air pollution and climate change, consumes huge amounts of oil, a limited resource, and can cause accidents when driven recklessly or by inexperienced drivers. It also creates traffic congestion when too many of them try to go in the same direction at the same time. It also has the potential to cause serious injuries and death when a driver is distracted or impaired.

The development of the automobile was accelerated by the introduction of new technological advances in the 1860s and ’70s, particularly Siegfried Marcus’s invention of a two-stroke internal combustion engine powered by gasoline. By the end of the century, engineering had been subordinated to questionable aesthetics and nonfunctional styling at the expense of safety and economy. By the mid-1960s, automobile manufacturers were delivering vehicles to retail buyers with an average of twenty-four defects per car, mainly safety-related. The era of the annually restyled road cruiser was ended with the imposition of federal standards for automotive safety, air quality and energy consumption; by increasing competition from Japanese automakers with small, economical, functionally designed cars that were reliable and durable; and by escalating gasoline prices following the oil shocks of 1973 and 1979.