The UEFA Champions League is UEFA's most prestigious club competition. It was originally created as the European Champion Clubs' Cup for the 1955/56 season, before its format and name were changed in 1992. Real Madrid CF have been the most successful side in the UEFA Champions League, winning the competition three times. They are also the most successful side overall with nine triumphs, followed by six for AC Milan and five for 2005 champions Liverpool FC.
The Champions League is open to each national association's domestic champions, as well as clubs who finish just behind them in their respective domestic championship. The number of clubs that can be entered by an association and their entry point in the competition depends on the association's position in UEFA's coefficient ranking list.
Since its inception in 1992/93, the Champions League has continued to evolve, maintaining a mixture of round-robin group matches as well as its traditional knock-out format. The current format was introduced in 2003/04. After three qualifying rounds, 32 teams contest the group stage, divided into eight groups of four. The group winners and runners-up advance to the knockout stages, the eight third-placed teams move into the UEFA Cup third round, and the eight fourth-placed teams are eliminated.
A draw determines who each of the 16 clubs will play in the first knock-out stage, with ties decided over two matches on a home and away basis. The club that scores the greater aggregate of goals advances, or in the event of both teams scoring the same number of goals, the team which scores more away goals. If the away-goals rule proves inconclusive, extra time of two periods of 15 minutes is played after the second match. If during extra time both teams score the same number of goals, away goals count double (ie the visiting team advances). If no goals are scored during extra time, the winner is decided by penalty kicks. The two teams that advance from the knock-out round contest the final, held as a single match in May.
The European Champion Clubs' Cup was a purely knockout competition until the format was changed in 1992/93 with the inception of the UEFA Champions League. That year the competition began with three knockout rounds with the winners advancing to a group stage involving two sets of four clubs playing home and away. The two group winners contested the final. A similar format was used the following season, with the addition of a two-legged semi-final stage involving the top two clubs from both groups.
The competition expanded further for the 1994/95 season with one preliminary round required before the clubs divided into four groups of four clubs. The top two clubs in each group advanced to the knockout stage, which this time began at the quarter-final stage. The 1997/98 season saw another phase of expansion. Two qualifying rounds were introduced and the group stage expanded to six groups of four clubs each. The six group winners and the two best runners-up advanced to the knockout stages.
An additional qualifying round was introduced for the 1999/2000 season to generate two group stages, firstly with 32 teams - eight groups of four - who played six matches apiece to reduce the competition to 16 teams for the second group stage, with the eight third-placed teams moving to the UEFA Cup third round. At the end of the second group stage, eight teams remained to contest the knock-out stage.