The UEFA Champions League (usually referred to as simply the Champions League or historically as the European Cup) is an annual association football cup competition organised by UEFA since 1955 for the top football clubs in Europe. The final of the competition is – along with the NFL's Super Bowl – the most watched annual sporting event worldwide, drawing just over 100 million television viewers.

Prior to 1992 the tournament was officially called the European Champion Clubs' Cup but was usually referred to as simply the European Cup or European Champions' Cup. The competition was initially a straight knockout competition open only to the champion club of each country. During the 1990s the tournament began to be expanded, incorporating a round-robin group phase and more teams. Europe's strongest national leagues now provide up to four teams each for the competition. The UEFA Champions League should not be confused with the UEFA Europa League, formerly known as the UEFA Cup.

The tournament consists of several stages. In the present format it begins in mid-July with three knockout qualifying rounds and a play-off round. The 10 surviving teams join 22 seeded teams in the group stage, in which there are eight groups consisting of four teams each. The eight group winners and eight runners-up enter the final knockout phase, which ends with the final match in May. Since the tournament changed name and structure in 1992, no club has managed consecutive wins. The winner of the UEFA Champions League qualifies for the UEFA Super Cup and the FIFA Club World Cup.

The title has been won by 21 different clubs, 12 of which have won the title more than once. The all-time record-holders are Real Madrid, who have won the competition nine times, including the first five seasons it was contested. Spain's La Liga and Italy's Serie A are marginally the most successful leagues, having amassed 12 wins, between two and three clubs respectively. The English league has produced 11 winners from four clubs. English teams were controversially banned from the competition for five years following the events at Heysel in 1985. Internazionale are the current champions, having beaten Bayern Munich 2–0 in the 2010 final.