United Indoor Football (UIF) was an indoor American football league in the United States that operated from 2005 to 2008. Ten owners from the National Indoor Football League, including one expansion and two from arenafootball2 (af2) took their franchises and formed their own league. The league was based in Omaha, Nebraska.

Arena football is a variety of eight-man indoor gridiron football. The game is played indoors on a smaller field than American or Canadian football, designed to fit in the same surface area as a standard North American ice hockey rink, resulting in a faster and higher-scoring game that can be played on the floors of indoor arenas. The sport was invented in 1981, and patented in 1987, by Jim Foster, a former executive of the National Football League and the United States Football League. The name is trademarked by Gridiron Enterprises and had a proprietary format until its patent expired in 2007.