In 1955-56, the first edition of Europe’s premier tournament, then called the European Champion Clubs’ Cup, took place. It was played on a knockout basis, with only four rounds (first round, quarterfinals, semifinals and final).
The following season, the competition changed to a group stage and was renamed Champions League. By 1992, the number of participating clubs had doubled to 32.
Since then, there have been a series of changes to the Champions League’s structure and rules. These have been designed to bring greater sporting and financial incentive to the league phase, create a better balance between teams from different countries in the knockout phase and increase the likelihood of reaching the final at a neutral venue.
UEFA has also tweaked the way that clubs qualify for the quarterfinals and semifinals, increasing the number of slots reserved for domestic champions from two to five. The slot is granted to a team that wins a four-round qualifying tournament open only to national champions from associations with coefficients below the top 10.
The new system does not introduce country protection in the knockout phase, meaning that it could be possible for Liverpool to play Chelsea. The draw for the round of 16 will also no longer use seeding pots, allowing clubs to be drawn together regardless of whether they are from the same association or have met certain stadium, infrastructure and finance criteria. It will instead rank the eight winners and runners-up from the groups in order of their league ranking, with a priority given to those who have won fewer away games.