Automobiles (also car, auto, or motorcar) are self-propelled vehicles that transport passengers. They typically have four wheels and use an internal combustion engine fueled by a volatile fuel. Automobiles are built in a wide range of shapes and sizes for various purposes, but they all share some basic components, such as the chassis, engine, drivetrain, and tires. In contrast, trucks and buses are designed primarily for the transport of goods and are constructed with heavier parts.

Most automobiles burn a fuel—typically gasoline, kerosene, diesel fuel, or liquefied petroleum gas (LPG)—to power an engine that drives the wheels. The engine’s energy is transferred to the wheels through a transmission, which also has a set of gears to adjust speed and torque. Some modern automobiles have additional features such as power steering, power brakes, and air conditioning.

The automotive industry has become one of the most important economic sectors in many countries. It is a major user of petroleum products and steel, and it employs millions of people around the world. It is a source of income for many ancillary industries, including those that manufacture batteries and tire rubber. Automobiles have radically changed the way that humans live and work. They allow people to travel far and often in great comfort, and they have brought them closer to the remote natural world. They have transformed the way that cities and rural areas are structured, making it possible for a large number of people to live in cities or suburbs while working outside the city and visiting family and friends in rural areas.

Karl Benz is credited with inventing the automobile in 1885, and others quickly followed with their own designs. By the 1920s, automobiles had overtaken horse-drawn carriages on roads and byways in Europe and America. The cars that came onto the market after World War I made it possible for the middle classes to own a car for the first time, and mass-production techniques introduced by American automotive manufacturer Henry Ford reduced the cost of cars even further.

The first automobiles were powered by steam, electricity, or gasoline engines. The steam engines could not move very quickly and were difficult to start, while electric cars had a limited range and recharging stations were scarce. In the end, the gas-powered automobile won out because it was economical, easy to operate, and relatively reliable.

Since then, the industry has continued to develop in response to technological advances, safety requirements, and consumer demands. Today’s cars are complex technical systems with thousands of subsystems that work together to keep them running safely and reliably. Research and development engineers are constantly seeking to improve the design of every part of an automobile, from the body to the internal combustion engine, to make them easier to operate and more environmentally friendly. Some of these improvements are the result of breakthroughs in technology, such as electronic computers and high-strength plastics, while others address new demands such as environmental regulation and consumer safety.