Automobiles are vehicles that carry people for personal transportation. They usually have four wheels and an internal combustion engine powered most often by gasoline, a liquid petroleum product. They are one of the most universal of modern technologies and are manufactured by one of the largest industries in the world. More than 73 million new automobiles were produced worldwide in 2017.

Karl Benz, a German engineer, is credited with inventing the automobile around 1885. He and others developed steam, electric and gasoline-powered vehicles before the 1920s when Henry Ford revolutionized manufacturing methods with the Model T, which made automobiles affordable for middle-class families. The automobile has transformed society in many ways, making modern life seem almost inconceivable without it. People can commute to work and school, go shopping, and take family vacations. The automobile also has influenced urban planning, government services, and even fashion.

In the United States, where most cars are driven, more than three trillion miles (five trillion kilometers) are traveled every year. Hundreds of different models of passenger cars are available, and manufacturers offer a wide variety of features to consumers. Many of these systems are aimed at improving safety and comfort. Some are optional; others are required by government regulations.

Various definitions of the automobile have popped up over the years, but most agree that it is a self-propelled motor vehicle designed for passenger transportation on land. Most of these vehicles use an internal combustion engine fueled most commonly by gasoline, although some use alternative fuels. Other engines include diesel and electricity. Some automobiles are built for commercial purposes, such as delivery trucks and buses.

The earliest automobiles were built for wealthy patrons, but as engineering and manufacturing improved, they became more affordable to most families. Henry Ford used the assembly line in his factories to speed production and reduce cost, making it possible for the Model T to be mass-produced and affordable to middle-class families. The Model T is considered the first car to be affordable for most American families and is regarded as one of the greatest inventions in history.

Automobiles are constantly evolving. Some of the most recent innovations include blind-spot monitoring and automated emergency braking, which help drivers avoid collisions and reduce driver fatigue. There are also newer engines that run on alternative fuels such as liquefied petroleum gas (LPG) and hybrid engines that combine the advantages of traditional engines with those of electric power.

Thousands of parts make up the modern automobile. Similar to the human body, these components are arranged into several semi-independent systems with specific functions. These include a circulatory system for coolant, lubricating oil and fuel. The arrangement of these systems and their relationship to each other depends on the intended purpose of the automobile. For example, a car that is intended for city driving will have a more compact and economical design than a sport car that needs to be fast and comfortable at high speeds.