Automobiles (or cars) are motor vehicles that have four wheels and use an internal combustion engine to run. They are usually built for passenger transportation and have seating for one to six people. There are many different types of automobiles. They are classified by their shape, size, propulsion system, engine type and layout and whether they operate on tracks, air, water, or road.

The automobile revolutionized the way Americans work, live and play. No other invention has had such a profound effect on the daily lives of Americans. It ended rural isolation, brought urban amenities (like schools and better medical care) to the countryside and created modern cities. It changed the architecture of American dwellings and altered the conception and composition of urban neighborhoods, making suburbia a reality. It ended the age of railroads and ushered in the era of auto-mobility.

In the early 1900s, a businessman named Henry Ford perfected the manufacturing process for cars and made them affordable for middle class families. The Ford Model T was an instant success. The automobile triggered new industries and jobs for those involved in car production, manufacturing, repairing and selling them. It also spawned leisure activities, such as restaurants, hotels and amusement parks.

Today, there are more than 1.4 billion cars in operation worldwide. They travel more than three trillion miles per year and are the primary means of transportation for most families in the world. As safety standards become increasingly stringent, manufacturers are forced to incorporate more sophisticated safety systems into their vehicles. Some of these technologies are available only on expensive luxury vehicles, but others—such as tire pressure monitoring and stability control—are now standard in most vehicles.