An automobile (or car) is a four-wheeled passenger vehicle designed and constructed principally for transportation on roads. Most definitions specify that a modern automobile is propelled by an internal combustion engine powered by a volatile fuel. The modern automobile is a complex technical system employing thousands of subsystems, each with specific design functions. These subsystems include the body, chassis, engine, drivetrain, control systems and safety systems.

Automobiles have profoundly changed the lives of their users and shaped the society in which they operate. They have revolutionized the way we work, play and socialize. They have boosted economic growth, helped to break down geographic boundaries, and spawned related industries such as gas stations and roadside restaurants. They have encouraged outdoor recreational activities and stimulated participation in organized sports, but they also have contributed to traffic congestion and pollution. They have created a new type of urban sprawl, with its attendant problems of housing and urban planning.

In the United States, automobiles first achieved widespread popularity in the 1920s and became a key force for change as the nation moved to a consumer goods-oriented economy. By the middle of the century, they ranked as the country’s largest value product and provided one out of every six jobs. They were the lifeblood of a petroleum industry and consumed large amounts of steel and other industrial products. They demanded the development of a whole series of ancillary industries and promoted changes in industrial technology.

The scientific and technical building blocks for the automobile date back several hundred years. Dutch scientist Christiaan Huygens invented a kind of internal combustion engine sparked by gunpowder in the late 1600s. By the end of the 19th century, steam cars could reach high speeds but were hard to start and had limited ranges. Electric-powered cars were relatively quiet and smooth, but their expensive batteries made them inaccessible to the mass market. Gasoline-powered cars, which could travel at a modest speed and were easy to start, won the day.

Henry Ford introduced the assembly line in 1913, making it simple for workers to produce many cars at once. His Model T runabout sold for less than the annual salary of a skilled worker and put automobiles within the reach of middle-class Americans.

Automobiles soon became the dominant mode of transportation, and America soon dominated the world’s auto markets. By 1966, the era of the annually restyled “road cruiser” had ended with governmental controls on automotive safety and air pollution; escalating gasoline prices; energy-efficient designs, such as those of the Japanese automakers; and the growing popularity of the smaller, lighter, more functionally designed and economically efficient compact sedans that now dominate world markets.

Whether it’s a sporty 2023 Mazda MX-5 Miata that delivers big fun in a small package or a practical and fuel-efficient Kia Niro hybrid, today’s automobiles provide a variety of choices for every taste and budget. But no matter what your choice is, you can be sure that automotive engineering will continue to bring exciting and useful new features and technological advances.