Automobiles are self-propelled vehicles that carry passengers or cargo. They have four to eight tires and are powered by an internal combustion engine or electric motor. The automotive industry is a large and important sector of the economy, and automobiles are one of the most common forms of personal transportation. The branches of engineering that deal with the manufacture and technologies of automobiles are known as automotive engineering.

The modern automobile is usually driven by a liquid-cooled, piston-type internal-combustion engine, which may be mounted on the front or rear of the vehicle. Some manufacturers use air-cooled engines, but these are less efficient than their water-cooled counterparts. The engine drives the wheels directly, but some vehicles have a transmission system that sends power to the front or to the rear axles, or to both. The automobile is typically fueled with gasoline, but diesel engines are also used (using heavier petroleum oil) for some heavy vehicles and some passenger cars.

Probably no invention affected everyday American life more than the automobile, which was the cornerstone of a new consumer goods-oriented society. It was the principal source of employment for the steel and petroleum industries and a major customer of many other industrial products. It enabled people to travel farther and faster than could have been achieved on foot, horseback or rail and it provided them with greater convenience for daily tasks.

It was the United States that took a lead role in automotive development, starting with the founding of Ford Motor Company in 1908. By adopting innovations such as the assembly line and paying his workers $5 a day—which was far higher than the average wage of the time—Ford made the automobile affordable to most Americans.

By the 1920s the automobile was one of America’s biggest exports and it was a key force in globalization as it became an indispensable part of most societies around the world. However, as production volume increased, quality began to deteriorate and engineering was subordinated to the questionable aesthetics of nonfunctional styling, which sacrificed fuel economy and safety. The greater unit profits that Detroit gained by producing gas-guzzling “road cruisers” also came at the social cost of increased air pollution and a drain on dwindling world petroleum reserves.

Automobile accidents have been recorded since the 1700s, with the first documented fatality occurring in 1771 when Joseph Cugnot crashed his steam-powered car into a wall in Paris. In the nineteenth century, safety concerns led to over-regulation and for decades the maximum speed of an automobile was limited to 4 mph (5 kph). The advent of the Model T in the early twentieth century allowed more people to own a car and increased demand contributed to the development of safer cars. The National Highway Traffic Safety Administration identifies the primary causes of automobile crashes as driver error, lack of attention or distraction and speeding. The agency has funded research to develop autonomous or driverless cars, which would eliminate the need for human control and reduce risk of accidents.