Football is a family of team sports that involve, to varying degrees, kicking a ball to score a goal. Unqualified, the word football normally means the form of football that is the most popular where the word is used. Sports commonly called football include association football (known as soccer in North America and Oceania); gridiron football (specifically American football or Canadian football); Australian rules football; rugby union and rugby league; and Gaelic football. These various forms of football share to varying extent common origins and are known as football codes.

There are a number of references to traditional, ancient, or prehistoric ball games played in many different parts of the world. Contemporary codes of football can be traced back to the codification of these games at English public schools during the 19th century. The expansion and cultural influence of the British Empire allowed these rules of football to spread to areas of British influence outside the directly controlled Empire. By the end of the 19th century, distinct regional codes were already developing: Gaelic football, for example, deliberately incorporated the rules of local traditional football games in order to maintain their heritage. In 1888, The Football League was founded in England, becoming the first of many professional football associations. During the 20th century, several of the various kinds of football grew to become some of the most popular team sports in the world.

Several of the football codes are the most popular team sports in the world. Globally, association football is played by over 250 million players in over 200 nations, and has the highest television audience in sport,  making it the most popular in the world. American football, with 1.1 million high school football players and nearly 70,000 college football players, is the most popular sport in the United States, with the annual Super Bowl game accounting for nine of the top ten of the most watched broadcasts in U.S. television history . The NFL has the highest average attendance (67,591) of any professional sports league in the world and has the highest revenue out of any single professional sports league. Thus, the best association football and American football players are among the highest paid athletes in the world.

Australian rules football has the highest spectator attendance of all sports in Australia. Similarly, Gaelic football is the most popular sport in Ireland in terms of match attendance, and the All-Ireland Football Final is the most watched event of that nation’s sporting year.