The National Football League (NFL) is the largest professional American football league. Thirty-two teams from American cities and regions form the NFL. The league's teams are divided into two conferences: the American Football Conference (AFC) and the National Football Conference (NFC). Each conference is then further divided into four divisions consisting of four teams. Each team is labeled East, West, North, and South.

Each team plays sixteen games over a seventeen-week period during the league's regular season. Generally, it continues from September to December. At the end of each regular season, six teams from each conference play in the NFL playoffs, a twelve-team single-elimination tournament that culminates with the NFL championship, the Super Bowl. This game is held at a pre-selected site which is usually a city that hosts an NFL team. One week later, selected all-star players from both the AFC and NFC meet in the Pro Bowl, currently held in Honolulu, Hawaii.

The NFL was formed in 1920 as the American Professional Football Association . The name National Football League was adopted in 1922. The NFL has the honor of being one of the major professional sports leagues of North America. NFL football is a descendant of rugby football which was introduced to to the United States by Canada in 1874. When McGill University in Montreal invited Harvard University to Quebec to play a new Canadian version of "rugby football", it was then transformed into American college football.

Professional football in the United States existed in 1892 William "Pudge" Heffelfinger was paid $500 by an athletic club in Pittsburgh to take part in a game. Football was given great attention in the next few decades at elite colleges on the East Coast. It resulted in spreading the professional game widely in the Midwest, particularly in Ohio.

In 1920, the American Professional Football Association was founded at a Hupmobile dealership in Canton, Ohio. Jim Thorpe was elected president. The group of eleven teams, all but one in the Midwest, was originally less a league than an agreement not to rob other teams' players. APFA members continued to play non-APFA teams in the early years.The APFA began releasing official standings in 1921. The group changed its name to the National Football League the next year. However, the NFL was hardly a major league in the '20s. Teams entered and left the league frequently.

With the exception of the Green Bay Packers, all of the small-town teams, had moved to or been replaced by big cities by 1934. The institution of an annual championship game in 1933 was one factor in the league's rising popularity .

The NFL was successful in solidifying its dominance as America's top spectator sport in the 1970s and '80s. In American culture, Its role has been very important. The Super Bowl became an unofficial national holiday and the top-rated TV program most years. Monday Night Football brought in high ratings by mixing sports and entertainment. It was first aired in 1970. In the late 1970s, many rules changes were introduced to attract the casual fan.

The biggest challenge to the NFL in the post-merger era was the foundation of the United States Football League in the early 1980s. The USFL was a well-financed competitor with big-name players and a national television contract. However, the USFL proved to be a failure and could not last more than three years. The NFL has expanded into new markets and ventures in recent years. A series of pre-season exhibition games, called American Bowls were started by the league in 1986. These games were held at international sites outside the United States. The league also formed the World League of American Football, (now NFL Europa), in 1991. It is a developmental league now with teams in Germany and the Netherlands. The league played a regular-season NFL game in Mexico City in 2005 and intends to play more such games in other countries. The NFL was successful in launching its own cable-television channel, NFL Network in 2003.

As of 2006, The NFL season features: A 4-game exhibition season (or preseason) running from late July to late August ;A 16-game, 17-week regular season running from September to December or early January ; A 12-team playoff tournament beginning in January culminating in the Super Bowl in early February.

In the NFL, players wear uniform numbers based on the position of their playing. The current system was instituted into the league to more easily identify players on the field by their position

as a means for fans and officials (referees, linesmen). Players who were already in the league at that date were grandfathered, and did not have to change their uniform numbers if they did not conform. Since that date, players are invariably assigned numbers within the following ranges, based on their primary position.