Brøndby IF is a Danish football club based in Brøndbyvester, Brøndby, on the western outskirts of Copenhagen. The club is also known as Brøndbyernes Idrætsforening, or Brøndby and BIF for short. The club was founded in 1964 as a merger between two local clubs and was promoted to the Danish top-flight football league in 1981. Brøndby IF has won 10 Danish Football Championships and 7 Danish Cups. Brøndby's most successful period was from 1985 to 2005 where, in twenty years, they won ten Danish Championships. In 1991, Brøndby reached the semi-finals of the UEFA Cup and became the first Danish club to ever reach a European semi-final. Since the founding of fellow Copenhagen club F.C. Copenhagen in 1992, the two clubs have had a fierce rivalry, and the matches between the two sides is called the Copenhagen Derby.