Automobiles, also known as cars, are wheeled passenger vehicles that use a motor to drive. They have become the primary means of transportation for many people in the world. As of 2004, there are about 590 million automobiles in operation worldwide. They travel over 3 trillion miles (5 trillion kilometers) every year.

The scientific and technical building blocks of the modern car go back several hundred years. Leonardo da Vinci designed a number of different transport vehicles in the 15th century, and in 1885 the German inventor Karl Benz developed the first true automobile. Since then, numerous cars have been produced by various manufacturers in countless styles and designs. Most modern automobiles are fueled by gasoline, which is converted to energy by an internal combustion engine. Only 12 to 30 percent of the energy in gasoline is actually used to propel the car; the rest is lost to friction and heat.

In the early twentieth century, automobiles caused sweeping changes in industry, society and everyday life. They changed how cities were built, how families lived together and where people worked.

As automobiles became more popular, new industries grew up to supply them with parts and fuel. These included auto manufacturing, rubber, and later plastics. Services like gas stations and convenience stores were also formed. The automobile allowed more people to move around and led to social changes, such as women getting the vote.

Despite these positive aspects, some people have criticised the automobile. Some have even compared it to a disease. For example, in his book Autokind versus Mankind (1971), Kenneth R Schneider argued that the automobile was destroying city centres and creating a culture of isolation and loneliness for urban dwellers. Other authors such as Booth Tarkington, whose books The Magnificent Ambersons and Free Air were written in the late nineteenth century, decried the changing world of automobiles.

By the end of the 1920s, however, the era of the automobile was beginning to come to an end. Market saturation coincided with technological stagnation, and engineering was being subordinated to the questionable aesthetics of nonfunctional styling at the expense of safety, economy and quality. By the mid-1940s, most major car manufacturers had introduced only minor improvements in their models.