The Bears have played in over a thousand games since becoming a charter member of the NFL in 1920. Through the 2005 season, they lead the NFL in overall franchise wins with 671 and have an overall record of 671–495–42 (going 657–479–42 during the regular season and 14–16 in the playoffs).

They were founded in 1919 by the A.E. Staley Company in Decatur, Illinois as the Decatur Staleys, originally as a company team, the typical start for several of the early professional football franchises. Staley hired George Halas and Edward "Dutch" Sternaman in 1920 to run the team and turned full control of the team over to them in 1921.

However, official team and league records call George Halas the founder as he took over the team in 1920 when it became a charter member of the NFL. The team relocated to Chicago in 1921, where the club was renamed the Chicago Staleys under an agreement that was reached by Halas and Sternaman with Staley. At the time when the franchise moved to Chicago, Halas purchased the rights for $100.

Halas liked the bright orange-and-blue colors of his alma mater, the University of Illinois, and the Bears adopted those colors as their own, albeit in a darker shade of each (the blue is a Navy Blue, and the orange is Pantone 1665, similar to burnt orange). As with several early NFL franchises, the Bears derived their nickname from that of their city's baseball franchise, in this case the Chicago Cubs.

After the money-losing 1932 Championship season, Halas's partner Dutch Sternaman left the organization. Halas maintained full control of the Bears until his death in 1983. He also coached the team off-and-on for forty seasons, an NFL record. For the most part, the Bears have stayed in the Halas family. The team is currently owned by Halas' daughter Virginia McCaskey and has been run on a day-to-day basis since 1999 by President and CEO Ted Phillips.

The Bears were responsible for triggering the NFL's long-standing rule that a player could not be signed until his senior class had graduated. The NFL took that action as a consequence of the Bears' aggressive signing of famous University of Illinois player Red Grange, within a day after his final game as a collegian.

The Bears became a dominant team in the early 1940s, reaching the NFL Championship Game five times during a seven season span, while winning four. The team acquired the University of Chicago's discarded nickname "Monsters of the Midway" as well as a newly-penned theme song that declared them "The Pride and Joy of Illinois". One famous victory during that period was their 73–0 victory over the favored Washington Redskins at Griffith Stadium in the 1940 NFL Championship Game. The score is still an NFL record for lopsided results.

The Bears declined in the late 1940s and continued to be on a down trend throughout the 1950s. The team did rebound in 1963 to capture their 8th NFL Championship under Halas. The late 1960s and early 1970s gave way to notable players like Dick Butkus, Gale Sayers, and Brian Piccolo, who died of lung cancer in 1969. The American television station, ABC filmed a movie about Piccolo in 1971.

In 1975 the Bears drafted Walter Payton with their first pick. Payton made an inital impact on the football landscape. He won the NFL Most Valuable Player Award in the 1977–78 season. Payton would go on to eclipse Jim Brown's NFL career rushing record in 1984. Payton would hold the NFL rushing total until 2002, when Emmitt Smith of the Dallas Cowboys broke his record. Payton's career and great personality would capture the hearts of Bear fans, who called him "Sweetness". Payton passed away from a rare liver cancer in 1999.

The Bears' rivalry with the Green Bay Packers is one of the oldest and fiercest in professional sports, dating back to 1921. In one infamous incident in 1921, Halas got the Packers expelled from the league in order to prevent them signing a particular player, and then graciously got them re-admitted after the Bears had closed the deal with that player. In the 1985 season, Coach Mike Ditka used 350-plus pound lineman "Refrigerator" Perry as a truly "wide" receiver in a touchdown play at Lambeau Field, flagrantly taunting the Packers. The Packers have also one-upped the Bears from time to time over the years, such as the "Instant Replay Loss" game of 1989.

The Bears have won a total of 9 league championships, including Super Bowl XX after the 1985 season in which they dominated the NFL with their then-revolutionary 46 defense and a cast of characters that recorded the novelty rap song "The Super Bowl Shuffle". The season was notable in that the Bears had only one loss, the "unlucky 13th" game of the season, a Monday night affair in which they were defeated by the Miami Dolphins. At the time, much was made of the fact that the Dolphins are the only franchise in history (through the 2005 season) to have an undefeated season and post-season. The Dolphins came close to setting up a rematch in the Super Bowl, but lost to the New England Patriots in the AFC title game. Ironically enough, "The Super Bowl Shuffle" was videotaped the next day after that Monday night loss.

After the 1985 Championship season, the Bears remained competitive throughout the 1980s but failed to return to the Super Bowl. After the firing of Mike Ditka at the end of the 1992 season, the Bears have only made the playoffs three times--winning only one game. They have been defeated at home in the playoffs twice in the new millennium, most recently in the 2005-06 season. The Bears have not played in the NFC Championship Game since 1988, when the San Francisco 49ers beat the Bears 28-3 at Soldier Field. The franchise believes that the trip to the 2005 playoffs is the stepping stone to returning to prominence of American football.