Automobiles are vehicles that are powered by engines and use the energy from burning a fuel to turn the wheels of the vehicle. Most cars burn gasoline or diesel, but other fuels are also used and there are even electric powered automobiles. The power produced by the engine is transferred to the driving wheels (caterpillars) through a transmission. The automotive industry is a vital economic force and provides one in six jobs in the United States.

The earliest automotive innovations go back hundreds of years. Leonardo da Vinci drafted theoretical plans for a motorized vehicle in the 16th century, and about 100 years later French engineer Cugnot developed his first steam-powered car. By 1920, the automobile had supplanted horse-drawn carriages as the dominant mode of personal transportation in Europe and North America. Henry Ford revolutionized industrial production techniques with the assembly line and lowered the price of his Model T to $575, well within the means of middle-class families.

The automobile is a key part of a consumer goods-oriented society, and it has helped create a new type of economic prosperity in the United States and throughout the world. It is also a major source of employment in the manufacturing sector and a big customer for ancillary industries, such as petroleum and steel. The automotive industry is also a leader in the development of technology and in promoting technological progress in other sectors of industry and society.

In recent decades, automobiles have become the most popular mode of personal transportation in many countries and are used by millions of people to commute to work or school and for leisure activities. The number of passenger cars in operation worldwide is estimated to be about 1.4 billion. In the United States alone, drivers travel over three trillion miles a year. Several hundred thousand new passenger vehicles are built each year.

Passenger cars come in a wide range of sizes and styles, from compact economy models like the Toyota Corolla to roomy sport-utility vehicles. There are also minivans and station wagons for families with children. During periods of stable fuel prices, manufacturers have produced a number of small, economical cars that are easy on the environment and gas budget.

Among the negatives of automobiles are the environmental impacts, particularly from the combustion of fossil fuels like gasoline. These emissions release carbon dioxide, a greenhouse gas, into the atmosphere. In the long term, this is a contributing factor to climate change and the depletion of natural resources.

Other problems associated with automobiles include the safety hazards, noise pollution and traffic congestion. In addition, the costs of maintaining and repairing a vehicle can be high. In the United States, there are nearly 90 million registered cars. Many families own more than one automobile, and some own as many as seven or more. In recent years, some automobiles have been marketed as green or ecological, but these models are still relatively rare. Changing trends, however, are likely to make such cars more common in the future.