Arena football is a variety of gridiron football played by the Arena Football League (AFL). It is a proprietary game, the rights to which are owned by Gridiron Enterprises, and is played indoors on a smaller field than American or Canadian outdoor football, resulting in a faster and higher-scoring game. The sport was invented in 1981, and patented in 1987, by James F. Foster, Jr., a former executive of the National Football League and the United States Football League. Though not the only variant of Indoor American football, it is the most widely known, and the one on which most other forms of modern indoor football are at least partially based.

Two leagues have played under the official arena football rules: the AFL, which played 22 seasons from 1987 to 2008 and resumed play under new ownership in 2010, and arenafootball2, the AFL's erstwhile developmental league, which played 10 seasons from 2000 through 2009.

While attending the Major Indoor Soccer League (MISL) All-Star game on February 11, 1981, at Madison Square Garden, Jim Foster came up with his version of football and wrote the rules and concepts down on the outside of a manilla folder, which resides at the Arena Football Hall of Fame. Over the next five years, he created a more comprehensive and definitive set of playing rules, playing field specifications and equipment, along with a business plan to launch a proposed small, initial league to test market the concept of arena football nationally. As a key part of that plan, while residing in the Chicago area, he tested the game concept through several closed door practice sessions in late 1985 and early 1986 in nearby Rockford. After fine tuning the rules, he then secured additional operating capital to play several test games in the MetroCentre in April 1986 and the Rosemont Horizon Arena in February 1987.