Automobiles are four-wheeled vehicles designed for passenger transportation and commonly propelled by an internal combustion engine burning a volatile fuel. They typically use gasoline (petrol), but can also be powered by electric, water, or diesel engines. Modern automobiles are complex technical systems, with many subsystems, such as those for control, safety, braking, and power distribution. The automotive industry is a major consumer of steel and petroleum, and an important contributor to technological change in the world.

The automobile revolutionized twentieth-century life. During the 1920s it became one of the most important economic forces, and an essential component of a new consumer goods-oriented society. It is now one of the largest industrial employers and provides a substantial percentage of the incomes of consumers in most developed countries. It is also the lifeblood of the petroleum and steel industries, and a significant user of many other industrial products. It is responsible for the development of assembly line production techniques, and has helped to revolutionize industrial manufacturing.

Automobile design depends largely on the vehicle’s intended use. Designs that are intended for off-road use require rugged, simple systems; those that are intended for high-speed highway travel must be optimized for passenger comfort and handling, and need advanced suspensions and control systems. The design of an automobile must take into account the weight of the vehicle and its contents, the relative position of the center of gravity, the type of wheels and suspension, and the distribution of weight between front and rear.