Automobiles are the primary mode of transportation in most countries. They enable people to live and work in different places, and they bring them closer to their loved ones, leisure activities and the natural world. In fact, most modern conveniences that we take for granted would be impossible to imagine without access to an automobile. Among them, the suburban home, drive-in movies and fast-food restaurants are all related to the automobile. Today, there are more than 1.2 billion cars in operation worldwide. The branch of Engineering that deals with the manufacture and technology of automotive vehicles is known as Automobile engineering.

Until the 1920s, only the wealthy had private cars. But Henry Ford revolutionized manufacturing with the moving assembly line, lowering the price of his Model T runabout to $575 in 1912—less than the average annual wage at the time. Within a decade automobile ownership had soared to 26 million Americans, and by the end of the century it had reached 60 million.

The automobile has made a significant contribution to the growth of cities, suburbs and interstate highway systems. It has also spawned new businesses, such as gas stations and auto parts stores. It has contributed to the decline of rural life and the demise of traditional agriculture, but has also accelerated urbanization by providing easy access to jobs, shops and services.

Cars are now the main form of personal transportation in most nations, with about three trillion miles (five trillion kilometres) being driven each year. Almost half of all households in the United States have an automobile, and most families own more than one.

In addition to the practical benefits of car ownership—which include increased work possibilities, wider choices for where to live in relation to work and social ties—there are psychological and emotional advantages. People who own cars are more independent than those who depend on public transportation, and they can avoid the stress of missing a bus or train.

A modern automobile contains several major systems that work together to control and power the vehicle. These are the engine, transmission, axles and wheels, brakes, electrical system, fuel system and other components. Each of these systems is subject to continuous improvement through technical advances.

The design of an automobile is determined to a large degree by its intended use. Vehicles for off-road use need rugged, durable systems that are resistant to severe overload and extreme operating conditions. On the other hand, vehicles that are designed to travel at high speeds on limited-access roads require passenger comfort options and optimized high-speed handling and stability.

Research continues into semiautonomous and autonomous vehicles, in which a computerized driving system greatly assists—or even replaces—the human driver. These systems will be used to control the basic functions of the car—such as acceleration, steering, braking and navigation—while the driver monitors and controls the entertainment system, radio, telephone and other devices. In this way, the automobile will become a truly mobile entertainment center.