Founded in 1992, the UEFA Champions League is the most prestigious continental club tournament in Europe, replacing the old European Cup. The competition runs from September to May, and in the group stage teams feature in a group of four and play each other home and away, with the top two progressing to the knockout stage. Thereafter, the 16 teams remaining take part in a knockout tournament until the winner is crowned in the final. The third-placed team is relegated to the Europa League, while the last-placed outfit is knocked out altogether. Qualification for the competition comes via league placement from the previous season, while qualifying rounds take place before the group stage for unseeded teams. One hundred and thirty-seven different clubs have competed since its inception, with Real Madrid winning the most titles (13). The competition's all-time leading goalscorer is Cristiano Ronaldo.