The UEFA Champions League, known simply as the Champions League, is an annual continental club football competition organised by the Union of European Football Associations (UEFA) and contested by top-division European clubs. It is one of the most prestigious tournaments in the world and the most prestigious club competition in European football, played by the national league champion (and, for some nations, one or more runners-up) of each UEFA national association. The final of the 2012–13 tournament was the most watched UEFA Champions League final to date, as well as the most watched annual sporting event worldwide in 2013, drawing 360 million television viewers.
While most of Europe's national leagues can still only enter their national league champion, Europe's strongest national leagues now provide up to four teams for the competition and will provide up to five teams from the 2015–16 season onwards.
In its present format, the UEFA Champions League begins in mid-July with three knockout qualifying rounds and a play-off round. The 10 surviving teams enter the group stage, joining 22 other teams qualified in advance. The 32 teams are drawn into eight groups of four teams and play each other in a double round-robin system. The eight group winners and eight runners-up proceed to the knockout phase that culminates with the final match in May.
Real Madrid is the most successful club in the competition's history, having won the tournament ten times, including its first five seasons. Spanish clubs have accumulated the highest number of victories (15 wins), followed by England and Italy (12 wins apiece). The competition has been won by 22 different clubs, 12 of which have won it more than once. Since the tournament changed name and structure in 1992, no club has managed consecutive wins; The reigning champions were Barcelona, who secured their fifth title in the competition after defeating Juventus 3–1 in the 2015 Final.