The league began play in 1920 and comprised five teams from Ohio (Akron Pros, Canton Bulldogs, Cleveland Tigers, Columbus Panhandlers, and Dayton Triangles), four teams from Illinois (Chicago Tigers, Decatur Staleys, Racine Cardinals 【the Cardinals were based in Chicago but took the name of a local street】, and Rock Island Independents), two from Indiana (Hammond Pros and Muncie Flyers), two from New York (Buffalo All-Americans and Rochester Jeffersons), and the Detroit Heralds from Michigan. Of these original franchises, only two remain: the Cardinals left Chicago for St. Louis after the 1959 season and relocated to Arizona in 1988; the Decatur Staleys moved to Chicago in 1921 and a year later changed their name to the Bears.

The NFL survived many years of instability and competition from rival organizations to became the strongest American professional football league. The most serious challenge to its leading role came from the American Football League (AFL) in the 1960s. The NFL and AFL completed a merger in 1970, creating a 26-team circuit under the name of the older NFL. Since then the league has expanded four times, adding six new franchises.

For a more complete history of football and the NFL, see football, gridiron.

The league's 32 teams are aligned as follows:

The league season culminates with an annual 12-team playoff tournament leading to the Super Bowl championship game. The NFL has headquarters in New York City and since 1963 has maintained the Pro Football Hall of Fame in Canton, Ohio.