Rosenborg Ballklub is an association football club based in Trondheim, Norway. The most successful club in Norway, Rosenborg has won the Norwegian Premier League 22 times and the Norwegian Football Cup 9 times. Although founded in 1917, it was not permitted to play in matches sanctioned by the Football Association of Norway until 1928. Rosenborg joined the top league in 1967 and won it in the club's inaugural top tier season. It has only spent one season outside the top tier since, which was in 1978.