Manchester United Football Club, commonly referred to as Man United (often stylised as Man Utd), or simply United, is a professional football club based in Old Trafford, Greater Manchester, England. The club competes in the Premier League, the top division in the English football league system. Nicknamed the Red Devils, it was founded as Newton Heath LYR Football Club in 1878, but changed its name to Manchester United in 1902. The club moved from Newton Heath to its current stadium, Old Trafford, in 1910.

Manchester United have won a record 20 League titles, 12 FA Cups, five League Cups, and a record 21 FA Community Shields. They have won the European Cup/UEFA Champions League three times, and the UEFA Europa League, the UEFA Cup Winners' Cup, the UEFA Super Cup, the Intercontinental Cup and the FIFA Club World Cup once each. In 1968, under the management of Matt Busby, 10 years after eight of the club's players were killed in the Munich air disaster, they became the first English club to win the European Cup. Alex Ferguson is the club's longest-serving and most successful manager, winning 38 trophies, including 13 league titles, 5 FA Cups, and 2 UEFA Champions League titles between 1986 and 2013. In the 199899 season, under Ferguson, the club became the first in the history of English football to achieve the European treble of the Premier League, FA Cup, and UEFA Champions League. In winning the UEFA Europa League under Jos Mourinho in 201617, they became one of five clubs to have won the original three main UEFA club competitions (the Champions League, Europa League and Cup Winners' Cup).

Manchester United is one of the most widely supported football clubs in the world and has rivalries with Liverpool, Manchester City, Arsenal and Leeds United. Manchester United was the highest-earning football club in the world for 201617, with an annual revenue of 676.3 million, and the world's third most valuable football club in 2019, valued at £3.15 billion ($3.81 billion). After being floated on the London Stock Exchange in 1991, the club was taken private in 2005 after a purchase by American businessman Malcolm Glazer valued at almost £800 million, of which over £500 million of borrowed money became the club's debt. From 2012, some shares of the club were listed on the New York Stock Exchange, although the Glazer family retains overall ownership and control of the club.

Arsenal Football Club is a professional football club based in Islington, London, England. Arsenal plays in the Premier League, the top flight of English football. The club has won 13 league titles (including one unbeaten title), a record 14 FA Cups, two League Cups, 16 FA Community Shields, the League Centenary Trophy, one European Cup Winners' Cup, and one Inter-Cities Fairs Cup. In terms of trophies won, it is the third-most successful club in English football.

Arsenal was the first club from the South of England to join the Football League in 1893, and they reached the First Division in 1904. Relegated only once, in 1913, they continue the longest streak in the top division, and have won the second-most top-flight matches in English football history. In the 1930s, Arsenal won five League Championships and two FA Cups, and another FA Cup and two Championships after the war. In 1970–71, they won their first League and FA Cup Double. Between 1989 and 2005, they won five League titles and five FA Cups, including two more Doubles. They completed the 20th century with the highest average league position. Between 1998 and 2017, Arsenal qualified for the UEFA Champions League for 19 straight seasons.Herbert Chapman, who changed the fortunes of Arsenal forever, won the club its first silverware, and his legacy led the club to dominate the 1930s decade; Chapman, however, died of pneumonia in 1934, aged 55. He helped introduce the WM formation, floodlights, and shirt numbers; he also added the white sleeves and brighter red to the club's jersey. Arsène Wenger is the longest-serving manager and won the most trophies. He won a record seven FA Cups, and his title-winning team set an English record for the longest top-flight unbeaten league run at 49 games between 2003 and 2004, receiving the nickname The Invincibles.

In 1886, munitions workers at the Royal Arsenal in Woolwich founded the club as Dial Square. In 1913, after the destruction of their South London stadium by suffragettes, the club crossed the city to Arsenal Stadium in Highbury, becoming close neighbours of Tottenham Hotspur, and creating the North London derby. In 2006, they moved to the nearby Emirates Stadium. With an annual revenue of £340.3m in the 2019–20 season, Arsenal was estimated to be worth US$2.68 billion by Forbes, making it the world's eighth most valuable club, while it is one of the most followed on social media. The motto of the club has long been Victoria Concordia Crescit, Latin for "Victory Through Harmony".