What is each club's pedigree? Who are their key players, new faces and ones to watch? UEFA.com has all the answers.
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UEFA coefficient ranking (end of 2018/19): 3
How they qualified: German champions
European Cup best: winners x5 (most recently 2013)
Last season: round of 16 (lost 3-1 on aggregate to Liverpool)
Group stage last season: Group E winners – W4 D2 L0 F15 A5 (v Ajax, Benfica, AEK Athens)
In: Lucas Hernández (Atlético Madrid), Benjamin Pavard (Stuttgart), Ivan Perišić (Inter, loan), Philippe Coutinho (Barcelona, loan)
Out: Franck Ribéry (released), Arjen Robben (released), Rafinha (released), Mats Hummels (Dortmund), Renato Sanches (LOSC Lille)
Coach: Niko Kovač
A defensive midfielder, Kovač represented Hertha, Leverkusen, Bayern and Croatia with distinction during his playing career. After a spell as Croatia coach – including at the 2014 FIFA World Cup – he resurfaced at Eintracht, whom he led to 2018 German Cup success against Bayern. Took the reins at the Bavarian club last season, winning a domestic double in his first campaign.
Key player: Robert Lewandowski
Lewandowski scored eight goals in Bayern's six group games last season and will be their focal point again this season, particularly now Franck Ribéry and Arjen Robben have left the club. Passed 200 Bundesliga goals last season and was top scorer in the league for the fourth time in his career. The Pole has never missed a penalty (9/9) in this competition.
One to watch: Alphonso Davies
Born in a Ghanaian refugee camp and raised in Canada, the 18-year-old winger sparkled in the spring after joining Bayern from Vancouver Whitecaps and impressed in pre-season.
UEFA coefficient ranking (end of 2018/19): 17
How they qualified: fourth in English Premier League
European Cup best: runners-up (2019)
Last season: runners-up (lost 2-0 to Liverpool in the final)
Group stage last season: Group B runners-up – W2 D2 L2 F9 A10 (v Barcelona, Inter, PSV)
In: Tanguy Ndombele (Lyon), Giovani Lo Celso (Real Betis, loan), Ryan Sessegnon (Fulham)
Out: Kieran Trippier (Atlético Madrid), Vincent Janssen (Monterrey), Fernando Llorente (released), Georges-Kévin Nkoudou (Beşiktaş)
Coach: Mauricio Pochettino
A tough-tackling central defender, Pochettino briefly turned out alongside Diego Maradona during his playing career. The Argentinian coached Espanyol and Southampton prior to his 2014 appointment at Tottenham, whom he has led to a top-four spot in each of the last four seasons. Took his team to the 2019 UEFA Champions League final too, despite making no signings in either transfer window last term.
Key player: Harry Kane
Top scorer at the 2018 FIFA World Cup, Kane – spearhead of the Tottenham attack – boasts the impressive return of 14 goals in just 19 career UEFA Champions League games. Twice the Premier League's Golden Boot winner, the 26-year-old has struck at least 24 goals in all competitions for five consecutive seasons.
One to watch: Giovani Lo Celso
Still only 23, the Argentinian midfielder has impressed with Paris and Real Betis since moving to Europe from Rosario Central in 2016. The industrious yet creative midfielder was one of the stars of the UEFA Europa League last season, scoring five times in seven games, and already has 19 caps for a country blessed with attacking talent.
UEFA coefficient ranking (end of 2018/19): 35
How they qualified: runners-up in Greek Super League, play-off winners (beat Krasnodar 6-1 on aggregate)
European Cup best: quarter-finals (1999)
Last season: #UEL round of 32 (lost 3-2 on aggregate to Dynamo Kyiv)
In: José Sá (Porto), Mathieu Valbuena (Fenerbahçe), Rúben Semedo (Villarreal), Bruno Gaspar (Sporting CP)
Out: Bibras Natcho (Partizan), Björn Engels (Reims), Andreas Gianniotis (Maccabi Tel-Aviv)
Coach: Pedro Martins
As a player, the midfielder spent much of his career at hometown club Feirense but also represented Vitória SC, Sporting CP, Boavista, Santa Clara and Alverca. Coached in the Portuguese third tier for several clubs before being promoted to a first-team role at Marítimo in 2010. Stints in charge at Rio Ave and Vitória SC followed before Olympiacos came calling in April 2018.
Key player: Guilherme
The Brazilian midfielder gained invaluable experience with Udinese and Deportivo La Coruña before joining Olympiacos in 2018. The 28-year-old's defensive awareness and tackling ability make him a vital component of Pedro Martins' outfit.
One to watch: Lazar Randjelovic
Capable of playing out wide or through the middle, the 22-year-old actually joined Olympiacos last summer from Radnički Niš. He returned to his former club on loan last season and that extra experience has served him well at the start of this campaign. Featured in four qualifiers, scoring twice in a 16-minute cameo against Krasnodar to all but seal his side's group stage place.
UEFA coefficient ranking (end of 2018/19): 88
How they qualified: Serbian champions, play-off winners (beat Young Boys on away goals, 3-3 on aggregate)
European Cup best: winners (1991)
Last season: group stage (fourth place)
Group stage last season: fourth in Group C – W1 D1 L4 F5 A17 (v Paris, Liverpool, Napoli)
In: Mateo García (Las Palmas), Tomané (Tondela), Njegoš Petrović (Rad)
Out: Dejan Joveljić (Eintracht), Aleksa Terzić (Fiorentina), Lorenzo Ebecilio (Júbilo Iwata)
Coach: Vladan Milojević
A product of the club's youth system, Milojević played much of his football in Greece for Panathinaikos and Iraklis Thessaloniki. Since hanging up his boots, he has coached several clubs and his first managerial success came when he guided Čukarički to the top tier, before winning the Serbian Cup in 2015. Taking charge of Crvena zvezda in 2017, his side has won the SuperLiga two seasons on the trot (2018, 2019) and reached the UEFA Champions League group stage last season.
Key player: El Fardou Ben Nabouhane
The Comoros international is much admired by coach Milojević, who brought the forward to Belgrade after previously signing him on loan during his spell at Panionios in 2016. Last season, he racked up 17 league goals and seven in the UEFA Champions League qualifying and group stages.
One to watch: Richmond Boakye
Having played in Italy, Spain, the Netherlands and China, the Ghanaian forward's most successful seasons have come in the Serbian capital – he converted 13 times in 15 league appearances last season. Re-signing for the club, following a short spell at Jiangsu Suning, he contributed three goals and an assist in the side's UEFA Champions League qualifying campaign.
Did you know
This is Bayern's 23rd season in the group stage – fewer only than Barcelona and Real Madrid (24).
This is Tottenham's fourth successive season in the group stage.
Bayern and Tottenham met in consecutive seasons in the 1980s. The German side won their 1982/83 UEFA Cup Winners' Cup second round tie, with Spurs gaining revenge in the third round on their way to winning the 1984 UEFA Cup final – their last European success.
Tottenham's only meetings with Olympiacos and Crvena Zvezda came in consecutive rounds of the 1972/73 UEFA Cup. Spurs progressed in both ties, winning the home legs but losing away.
Crvena Zvezda beat Bayern in the semi-finals of the 1990/91 European Cup, triumphing 2-1 in Munich before a 2-2 home draw; they went on to beat Marseille on penalties in the final.