When is the draw?
The draw begins at 4pm BST on Thursday in Geneva.
How does it work?
Eight groups of four teams will be drawn. The teams are first split into four seeding pots and each group will have one team from each pot.
No teams from the same country can face one another and clubs from Russia and Ukraine will be kept apart.
The identity of 29 teams is known and the final three places will be determined in the second legs of the remaining play-offs on Wednesday night.
How are the pots decided?
Pot one consists of the holders (Bayern Munich), the Europa League winners (Sevilla) and the champions of the nations ranked highest by Uefa who have not earned a place by winning either of those tournaments. Pots two to four are are determined by the club coefficient rankings.
Which clubs are in which pot?
Pot one: Bayern, Sevilla, Real Madrid, Liverpool, Juventus, Paris Saint-Germain, Zenit Saint Petersburg, Porto.
Pot two: Barcelona, Atlético Madrid, Manchester City, Manchester United, Shakhtar Donetsk, Borussia Dortmund, Chelsea, Ajax.
Pot three: Dynamo Kyiv, RB Leipzig, Internazionale, Olympiakos, Lazio, Atalanta, and two more teams to be determined after Wednesday’s play-offs.
Other teams who have qualified: Lokomotiv Moscow, Marseille, Club Brugge, Borussia Mönchengladbach, Istanbul Basaksehir, Rennes, Ferencvaros.
Remaining play-offs (first-leg score in brackets): FC Midtjylland (0) v Slavia Prague (0); Red Bull Salzburg (2) v Maccabi Tel-Aviv (1); PAOK Salonika (1) v FK Krasnodar (2).
When are the group games?
They will be played on 20-21 October, 27-28 October, 3-4 November, 24-25 November, 1-2 December and 8-9 December.
More information: THE GUARDIAN.