The UEFA Champions League, commonly known as the Champions League, is an annual club association football competition organised by the Union of European Football Associations (UEFA) that is contested by top-division European clubs. The competition begins with a round robin league phase to qualify for the two-legged knockout rounds and the single-leg final. It is the most-watched club competition in the world and the third most-watched football competition overall, after the FIFA World Cup and the UEFA European Championship. It is one of the most prestigious football tournaments in the world and the most prestigious club competition in European football, played by the national league champions of their national associations.