It's going to be a dramatic departure from what fans are used to, so here's a full breakdown of what this means for football's top club competition.
What's going to be different about the Champions League?
From next season, 36 clubs will take part in the Champions League and they will all be in one big league table. The old (current) format saw 32 clubs divided into eight groups of four teams.
There will still be a draw at start of the season, but only to create the league-phase fixtures: eight games for each club, four at home and four away.
The 36 teams will be divided into four pots of nine. Pot 1 will have the titleholders of the UCL and the eight clubs with the best coefficients. The champions of the top domestic leagues and the UEL titleholders will no longer be prioritised for Pot 1. Pots 2 to 4 are ordered on club coefficient.
Each club will be drawn to play two teams from each pot -- one home, one away. So, unlike in the current format, a club in Pot 1 will play a game against two other clubs from Pot 1.
As a general rule, clubs from the same association will not be drawn against each other. However, to avoid deadlocking, the leagues with four or more clubs could play one match against another team from the same country.
From the final table, the top eight go direct to the round of 16. Positions nine to 24 will enter a playoff to earn the other eight places in the round of 16. Positions 25 to 36 are eliminated from Europe. There is no country protection in any of the knockout rounds.
Unlike in previous seasons, there is no drop down of teams from the Champions League to the Europa League after the league phase. Once eliminated, your European season is over.
There will be only one knockout-round draw for the round of 16 onwards, with teams seeded based upon their final league-phase position and no country protection. It means it's important where you finish in the table; the higher you are, the more favourable knockout route you will have -- on paper at least.
Why is this all happening?
More games equals more money, and the biggest clubs always take a larger slice of the broadcasting revenues. The top teams also want to play more meaningful games against their main rivals, which this should create at an earlier stage of the Champions League.
So does this mean more games?
Under the original plan proposed in 2021, the tournament was to almost double in size, from a total of 125 games to 225, with each team playing 10 games in the group stage.
However, that has now been scaled back to eight group stage fixtures, meaning a total of 189 games in the season.
It means two extra matchdays will be needed for the Champions League group stage.
The group stage will now finish at the end of January, rather than in December.
So what is the 'Swiss model'?
Rather than teams being drawn into eight groups of four, as is the case now, all clubs are placed into one giant table based on points, and then goal difference.
It is based on the Swiss-system tournament used in chess, whereby each team does not play all of the others. The chess format decides a team's next opponents after each set of games, whereas in the Champions League all group stage fixtures will be known at the start of the season.
It has been used in football in other competitions with a large number of participants, including in the Concacaf Nations League qualifying competition where all teams played four matches but the results were fed into one league of 34 nations.
Where do the 4 extra teams come from?
The number of clubs will be raised from 32 to 36. The new format means teams are guaranteed a minimum of eight games, and most will play at least 10.
2 places will go to the best performing leagues in Europe in this current season. The place goes to the next team in the league which has not automatically qualified. Last season, that would have been Liverpool and Atalanta. These places are most likely go to clubs from the top leagues.
1 place will go to the third-placed team in the league ranked fifth in the UEFA coefficient (this is effectively the average performance of all its clubs in Europe.) Last season that was France, so Marseille would have gone direct to the UCL group phase, with Stade Rennais promoted from the Europa League into UCL qualifying. However, the Netherlands overtook France into fifth at the start of this season, so the Eredivisie could get the extra place for the 2024-25 domestic season.
1 place will go to the qualifying path for champions. Four teams used to come through this route into the league phase, but from next season it will be five. The place cannot go to a team from the top 10 leagues as their champions do not go through qualifying.
At one stage, this was to be awarded to the highest-ranked champions (by UEFA coefficient) not to qualify for the group stage automatically. However, UEFA changed this to make it a qualifying berth rather than coefficient-related which would have benefitted Shakhtar Donetsk in most seasons due to their own high rating, despite Ukraine's falling league coefficient.
What happened to the places based on historical performance?
Originally, two places were to be reserved for the clubs with the highest five-year UEFA coefficient who failed to qualify for the Champions League.
Although a club would have to qualify for Europe to be eligible, it still meant that there could be leapfrogging. For instance, Manchester United could finish 8th in the Premier League, win the FA Cup and be promoted into the Champions League based upon their five-year coefficient. Man United would therefore jump above the team that finished in fifth to play in the UCL.
It was decided this method would not "fully in line with the values and solidarity-based European sports model" with qualifying based on sporting merit.
Who will benefit from the two coefficient places?
At the time the changes were announced the Netherlands would have gained an additional place in the Champions League. It piqued interest, as it was a berth going to a team not from the "Big Five" leagues. However, historically this is an outlier.
If we look back at the previous seven seasons, England and Spain take 11 of the 14 slots.
2022-23: England and Italy
2021-22: England and the Netherlands
2020-21: England, Spain
2019-20: Spain, Germany
2018-19: England, Spain
2017-18: England, Spain
2016-17: Spain, England
The Dutch Eredivisie would have benefitted in 2021-22 as it had three clubs in the group stage of the Europa Conference League (UECL), all of whom advanced. Feyenoord reached the final, just enough to get the Dutch second place in the coefficient table. In the five seasons before the UECL, the Dutch had been placed 5th, 8th, 7th, 29th and 9th.
If a country gets a coefficient place, that's an additional team in Europe. So, for instance, the Premier League would get eight places, with non-UCL positions dropping down one.
Champions League: 1-5
Europa League: 6, FA Cup winners
Europa Conference League: Carabao Cup winners
If the cup winners finish in the top 6, the places could drop to 7th and 8th in the table.
So the Premier League is pretty much nailed on for five UCL places?
English clubs have been dominant and have comfortably been in the top two leagues in the past three seasons. It's looking good, but there's a twist.
The Premier League will have eight clubs in Europe this season, as West Ham United won the UEFA Europa Conference League and didn't qualify for Europe domestically; it means every win by an English club will be worth slightly less to the coefficient score because it's an average of eight clubs rather than seven.
The last time England had eight clubs in Europe, in 2015-16, it only finished third in the season's coefficient ranking -- though both Southampton and West Ham failed to make it through the qualifying rounds. This season, all eight teams will take part in the group stages of one of the three competitions.
England's place was further strengthened when LaLiga side Osasuna failed to make the group stage of the Europa Conference League. On only two occasions in the past eight seasons has a league finished in the top two coefficient places without a full set of teams in the group stage -- both times being the Premier League: 2018-19 (Burnley did not qualify), 2015-16 (West Ham did not qualify.)
All things considered, it would take a very poor season for the Premier League not to get five places. Brighton & Hove Albion and Villa, along with Newcastle United who could be handed a difficult Champions League group, would have to struggle badly to put England's fifth spot in serious doubt.
When will we find out who gets the extra places?
In many seasons it may be obvious in March, once we know which leagues have teams through to the quarterfinals of the three European competitions.
However, the 2019-20 season shows that it can go right down to the wire. Germany didn't overtake the Premier League for second place until Bayern Munich beat Paris Saint-Germain 1-0 in the final of the Champions League. If that's repeated this season, we wouldn't know which league gets the second additional spot until the UCL final takes place June 1.
It would leave two clubs in the domestic leagues praying for the right result in the final. In 2019-20, Bayer Leverkusen and Leicester City finished fifth in Germany and England respectively. Leverkusen would have needed Bayern to win the UCL final to get the place, while Leicester required Bayern to lose the match.
What's the maximum number of places the Premier League can have in the UCL?
Under the old system, a maximum of five clubs from one association could play in the Champions League. It meant that in the unlikely event teams from the same league won the Champions League and Europa League, yet both finished outside the UCL places domestically, then fourth would have to surrender their place and drop into the UEL.
It's now possible that seven Premier League teams could earn a place in the UCL: The top five, and the winners of the UCL and the UEL.
It would also technically be possible to have 11 Premier League teams in Europe: The usual allocation of seven, plus the extra Champions League place and the titleholders of all three European competitions (if they finished outside a European position.)
UEFA has yet to take a decision on a maximum number for either. Sources have told ESPN that the UEFA ExCo meeting in the first quarter of 2024 is likely to finalise these numbers, and if there is a limit how it would affect other clubs from that league.
How will they decide the fixtures?
UEFA will create four pots of nine teams. The UCL titleholders will be in Pot 1, with all other pots filled according to the five-year club coefficient.
Each team will play two teams from each pot (one home, one away) to create an eight-match fixture list of roughly equal strength.
More "big matches" are created by the teams in the top pots being drawn against each other, which wasn't possible under the current system.
For instance, the teams in Pot 1 would draw two other clubs from Pot 1, 2, 3 and 4. Teams from the same association still cannot play each other in the group stage -- apart from leagues with 4+ teams who could play one other team from their country, if the draw puts them together.
This is how the seeding pots would look, based on a 36-team Champions League intake using the new system and the teams who would have qualified in the 2023-24 season.
Pot 1: Manchester City, Bayern Munich, Liverpool, Real Madrid, Paris Saint-Germain, Manchester United, Barcelona, Internazionale, Sevilla
Pot 2: Borussia Dortmund, Atletico Madrid, RB Leipzig, Benfica, Napoli, FC Porto, Arsenal, Shakhtar Donetsk, FC Salzburg
Pot 3: Atalanta, Feyenoord, AC Milan, Braga, PSV Eindhoven, Lazio, Red Star Belgrade, FC Copenhagen, Young Boys
Pot 4: Real Sociedad, Marseille, Galatasaray, Celtic, Molde, Newcastle United, Union Berlin, Antwerp, Lens
So, Manchester United could have a "Swiss Model" fixture list of: Bayern Munich, Paris Saint-Germain, Napoli, Atletico Madrid, Braga, Red Star Belgrade, Marseille and Celtic.
What about the Europa League and the Europa Conference League?
Both competitions will also switch to the Swiss Model from 2024, and will increase in size from 32 teams to 36.
There will be eight group-stage games in the Europa League, but only six in the Europa Conference League.
There will again be playoffs to reach the round of 16, but no drop down for the losers from the Europa League into the Europa Conference League either.
This is good news for the teams that took place in the group stage. One of the four Europa League semifinalists this season dropped down from the Champions League, and two of the Europa Conference League final four were in the Europa League group stage.