Automobiles are four-wheeled vehicles used primarily for passenger transportation, powered by an internal combustion engine using a volatile fuel. These vehicles have become the primary mode of land transport in the developed world, with 1.4 billion cars in operation today and traveling more than three trillion miles (five trillion kilometres) each year. The modern automobile is a complex technical system employing several subsystems that have specific design functions.

The invention of the automobile revolutionized many aspects of human life, giving people the freedom to travel and do more things in their free time. Before the automobile was invented, most trips were taken by train or boat or carriage. The automobile made it possible for people in the city to visit the countryside and vice versa.

In the first half of the 20th century, American firms dominated the industry, thanks to the innovations introduced by Henry Ford and others on the assembly line. This new production process made it easy to produce and sell millions of cars. The car became an indispensable tool for modern life and the middle class grew.

The design of a car depends on its intended use. For example, an automobile designed for off-road use should have simple systems that are resistant to overloads and extreme operating conditions. On the other hand, vehicles that are designed for highways should be light and aerodynamic to improve high-speed handling and vehicle stability. In addition, the body should provide passengers with clear visibility.