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 since 1992. It replaced the European Champion Clubs' Cup, or simply European Cup, which had run since 1955, adding a group stage to the competition and allowing multiple entrants from certain countries. It is one of the most prestigious tournaments in the world and the most prestigious club competition in European football. 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.
Before 1992, the competition was officially called the "European Champion Clubs' Cup", but was usually referred to simply as the "European Cup". It was initially a straight knockout tournament open only to the champion club of each country. During the 1990s, the format was expanded, incorporating a round-robin group stage and more teams. 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.