The new UEFA Champions League format explained

The updated version of the Champions League will see 36 clubs feature in the competition proper, an increase from 32 under the old format. There is an extra place for the fifth-best European league according to UEFA's ranking, which means France's Ligue 1 now has three automatic qualifiers.
In addition, there is an extra berth for each of the two leagues with the highest coefficient ranking from last season in UEFA competition, which this year are Germany and Italy. The remaining extra slot goes to a national champion to emerge from the qualifying rounds, which will be completed this midweek.
Since 2003, the Champions League featured 32 clubs split into eight groups of four, with the top two from each section advancing to the last 16. That has now changed radically, and from this season the 36 clubs will be pooled together in one league, in a so-called 'Swiss system' more commonly associated with chess.
Before, participating teams played six games in the group stage, facing each opponent home and away. Now clubs will each have eight games. The 36 teams will be split into four seeded pots of nine. Every club will play two teams from each pot, one at home and one away.
This "raises the prospect for fans of seeing the top teams go head to head more often and earlier in the competition," UEFA say, a nod to the fact this format was introduced at a time when the spectre of a breakaway Super League hung over European football. No team will come up against another club from the same domestic league as them, and every club can only face a maximum of two teams from any one country.
Whereas in past years the group stage ended in December, the expansion of the Champions League means the two extra matchdays will be staged in January. The number of games is increasing from 96 in the old group stage, up to 144 in the new league phase.
The 36 clubs will be ranked together in the one league, with the top eight all progressing to the last 16 and the format of the competition from that point on remaining the same. However, it will be seeded, taking into account positions in the league phase.
In addition, a play-off round will be introduced, with the teams finishing from 9th to 24th in the league phase going through to a two-legged knock-out tie to decide the remaining spots in the last 16. These play-off ties will be seeded. The bottom 12 teams in the league phase will be eliminated, with no access to the second-tier Europa League, as was the case in the past.