Introduced in 1955 as the Coupe des Clubs Champions Européens and commonly known as the European Cup, it was originally a direct play-off tournament open only to the champions of Europe's domestic leagues, with the winner being considered the European club champion.
The competition took its current name in 1992, adding a round-robin group stage in 1991 and allowing multiple entries from certain countries from the 1997–98 season.
It has since been expanded, and while most European domestic leagues can still only enter their champion, the strongest leagues now provide up to four teams.
Clubs finishing next in their domestic league and not qualifying for the Champions League are eligible to participate in the second-tier UEFA Europa League tournament and, from 2021, in the third-tier UEFA Europa Conference League.
In its current format, the Champions League begins at the end of June with a preliminary round, three qualifying rounds and a knockout round, all consisting of two legs.
The six surviving teams advance to the group stage, joining the 26 pre-qualified teams.
The 32 teams are divided into eight groups of four teams and play each other in a double round robin.
The eight group winners and eight runners-up progress to the knockout stage, culminating in a final match in late May or early June.
The winner of the Champions League qualifies for next year's Champions League, UEFA Super Cup and FIFA Club World Cup.
Spanish clubs have the most wins, followed by England and Italy.
England has the highest number of winning teams, with six clubs winning the title.
The competition was won by 23 clubs, 13 of which won it multiple times and eight successfully defended their title.
Real Madrid is the most successful club in the competition's history, having won it 14 times, including its first five seasons and five of the last ten.
Only one club has won all of its matches in a single tournament on its way to winning the tournament: Bayern Munich in the 2019–20 season.
Only two teams in the tournament's history have won the tournament by playing the final in their own stadium: Real Madrid at the Santiago Bernabeu in 1957 and Inter Milan at the San Siro in 1965.