The UEFA Champions League is the biggest competition among professional soccer teams in the world. By the time the group stage starts, 32 sides battle it out to claim one of the most treasured titles in the sport. Here is how the tournament works.

Teams qualify for the UEFA Champions League based on how they finish in their leagues. The champion of each of 13 leagues automatically earns a spot in the group stage. Six of those leagues also qualify their second place teams, while three have their third place teams in an automatic spot. Those three are the English Premier League, Italian Serie A, and the Spanish La Liga. The other forty associations, as well as other qualifying teams, battle through a series of playoff qualifiers to earn the final ten spots in the group stages.

The group stage has eight groups of four teams. Those four teams play a round robin of home and home games, meaning each team plays six total games. The top two teams after those matches advance to the knockout stage. A random draw is conducted. Once the field is set, the teams play a home and home, with the winner determined by an aggregate score. If there's a tie, the team with more road goals advances. If the road goals are even, then two fifteen minute extra time periods occur, followed by a shootout. This format continues up until the final, which is a single match at a neutral site. Extra time and penalty kicks are used as needed.

Real Madrid has the most Champions League titles with nine, the most recent coming in 2002. Italian side AC Milan has seven championships, while Liverpool has won five. The Champions League began in 1956 with Real Madrid winning. It was renamed as the Champions League in 1992.