Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. 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. It is widely considered to be the most prestigious football club competition in the world. The final of the competition is 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.