Almost everywhere in the world, cars are the main form of personal transportation. Although there are disadvantages to owning a car, most people find that it makes life easier in many ways. For example, a person can go to work or school whenever he wants without worrying about getting up early to catch the bus. People can also choose when to go shopping and do other things without having to worry about the schedule of the public transport service.

The automobile has come to symbolize both the promise and the problems of modern civilization. It has brought the conveniences of urban living and a new lifestyle to many people, but it also has contributed to suburbanization and to the decline of small farms in the United States. The automobile has stimulated participation in outdoor recreation and led to the development of highways linking cities and towns to rural areas and from region to region. It has brought many urban services—schools, hospitals, shops, and recreational opportunities—to the countryside and spawned new industries such as service stations, motels, and roadside restaurants. The automobile has become the dominant means of travel in the world, with 1.4 billion vehicles in operation worldwide.

Most modern automobiles use a four-stroke internal combustion engine, which burns fuel (such as gasoline or diesel) to produce energy that turns the wheels of the car. The power is transferred from the engine to the wheels through a transmission. The first automobiles burned wood or coal, but they soon used the much safer gaseous fuels that are available today. Karl Benz, a German engineer, is credited with inventing the automobile in 1885. He built a crude vehicle that had no seats or steering, but did have a gasoline-powered internal combustion engine. Gottlieb Daimler built an improved engine in a car in 1886.

Henry Ford, a businessman and an inventor, was the next to bring a practical automobile to the mass market. At his factory in Highland Park, Michigan, he innovated the modern assembly line and reduced the price of his Model T so that it could be afforded by middle-class families.

Automobile design depends on the type of vehicle and its intended use. For example, off-road automobiles must have rugged systems that can withstand heavy loads and severe operating conditions. On the other hand, passenger cars for highway use must have features that maximize passenger comfort and safety, as well as optimized engine performance and high-speed handling. The automobile is also a complicated machine with numerous parts that must be designed and assembled to ensure safety, reliability, and comfort. For the most part, however, engineers have subordinated engineering to nonfunctional styling, and quality has deteriorated to the point where in the mid-1960s American-made cars were delivered with an average of twenty-four defects per unit. In recent years, manufacturers have improved their designs and production processes. Some are producing hybrids, which combine a gas-powered engine with an electric motor. This can reduce emissions and improve fuel efficiency.