Most important player: Neymar. If he can rediscover his best form then he could be the difference between topping the group and failing to make it out into the knockouts.
How did they qualify: French League winners
Champions League pedigree: They have never won the competition and they have a recent history of choking, most recently against Manchester United but before that Barcelona.
Manager: Zinedine Zidane
Most important player: Eden Hazard. Making his return to football after injury it has been a slow start to Hazard's Real career. He is essentially the replacement for Cristiano Ronaldo a year too late.
How did they qualify: Third in La Liga.
Champions League pedigree: They are the most successful club in the tournament, having won it 13 times and three times consecutively under Zidane.
Manager: Philippe Clement
Most important player: Hans Vanaken, their creative attacking midfielder.
How did they qualify: Runners-up in Belgian First Division A
Champions League pedigree: They reached their peak in the seventies, when they reached the quarter-final in 1977 and were defeated finalists the following season.
Manager: Fatih Terim
Most important player: Ryan Babel. The resurgent Dutch forward is the spearhead of the national side and could play his way back into the major European leagues with an impressive performance in the Champions League.
How did they qualify: Super Lig champions
Champions League pedigree: They've never won the Champions League, but they have had European success with the 2000 UEFA Cup.
FC BAYERN MUNICH
Manager: Niko Kovac
Most important player: Robert Lewandowski. Lewandowski has been linked with a move away from Bayern for the past two years but in the absence of Franck Ribery and Arjen Robben he is now the undisputed figurehead.
How did they qualify: Bundesliga winners
Champions League pedigree: Bayern have won the Champions League five times, the UEFA Cup once and the Cup Winners' Cup once to be the most successful German team in European competition.
Manager: Mauricio Pochettino
Most important player: Harry Kane. Perhaps England's best player. His goals have given Pochettino the chance to develop younger players, and could give Tanguy Ndombele and others the chance to settle into the side.
How did they qualify: Fourth in the Premier League
Champions League pedigree: Spurs have won the UEFA Cup twice and the Cup Winners' Cup once, but the closest they have come to winning the Champions League was last season's defeat to Liverpool.
Manager: Pedro Martins
Most important player: Ruben Semedo. Now out of jail he has the chance to put his career back on track at 25.
How did they qualify: Runners-up in the Greek Superleague
Champions League pedigree: The closest they have come to European success is winning the Balkans Cup in 1963, and have never got past the UCL quarter-finals.
Manager: Vladan Milojevic
Most important player: Marko Marin. Unable to break through into the Chelsea side he moved to Olympiacos after several loan spells before moving to Red Star where he has impressed with his goalscoring as a midfielder.
How did they qualify: Champions of Serbian SuperLiga.
Champions League pedigree: They famously won the 1991 European Cup but have never challenged since.
Manager: Pep Guardiola
Most important player: Kevin De Bruyne. If he can stay injury free then he can unlock any defence. However Raheem Sterling could probably claim to be the exceptional player right now, and appears more physically resilient too.
How did they qualify: Premier League winners
Champions League pedigree: City have little European pedigree but as they have almost limitless financial resources that will likely change in the near future.
Manager: Luis Castro
Most important player: Taison. The experienced Brazilian is at the heart of the Donetsk side, and has played 237 games for the club while scoring 42 goals.
How did they qualify: Ukrainian Premier League champions
Champions League pedigree: They've barely dented the competition, but were UEFA Cup winners in 2009.
Manager: Nenad Bjelica
Most important player: Dani Olmo. The Spanish under-21 winger has impressed in Croatia since his surprise move from the Barcelona youth team.
How did they qualify: Croatian First League champions
Champions League pedigree: Dinamo's most successful showing in Europe came in 1961, when they reached the semi-finals of the European Cup Winners' Cup.
Manager: Gian Piero Gasperini
Most important player: Marten de Roon. The midfielder is at the heart of recent improvements with the Dutch national side.
How did they qualify: Third in Serie A
Champions League pedigree: This is their first season in the Champions League
Manager: Maurizio Sarri
Most important player: Cristiano Ronaldo. If he keeps up his ridiculous form into his 35th year then few other teams will stand a chance.
How did they qualify: Serie A winners
Champions League pedigree: They have won the Champions League twice, but the last win came in 1996. This is the best team they have had since their demotion, so could be the year to complete a hat-trick.
Manager: Diego Simeone
Most important player: Joao Felix. The Portuguese youngster will be considered Antoine Griezmann's talismanic replacement already.
How did they qualify: Second in La Liga
Champions League pedigree: They've won the Europa League three times and the Cup Winners Cup once. However they have been beaten finalists in the Champions League three times, and have never won it.
BAYER 04 LEVERKUSEN
Manager: Peter Bosz
Most important player: Kai Havertz. The 20-year-old midfielder has already been capped five times by the German national side.
How did they qualify: Fourth in the Bundesliga
Champions League pedigree: They were runners-up in 2002, and won the UEFA Cup in 1988.
Manager: Yuri Semin
Most important player: Joao Mario - The midfielder on loan from Inter Milan could add the quality to make it awkward for the better known teams in the group.
How did they qualify: Second in the Russian Premier League.
Champions League pedigree: Cup Winners' Cup semi-finalists in 1998 and 1999.
Manager: Jurgen Klopp
Most important player: Mo Salah. If the Egyptian repeats his form of last season there is every chance that he can blow away any opposition in front of Liverpool.
How did they qualify: Champions League winners, Premier League runners-up
Champions League pedigree: The most successful English side in Europe, with six European Cups/Champions League to their name.
Manager: Carlo Ancelotti
Most important player: Kalidou Koulibaly. The excellent central defender could be on the cusp of a huge move at the end of the season if he is a rock at the back yet again.
How did they qualify: Serie A runners-up
Champions League pedigree: Despite being regulars in the competition over the past decade, Napoli have yet to make it past the last-16.
RED BULL SALZBURG
Manager: Jesse Marsch
Most important player: Smail Prevljak. The 24-year-old Bosnian midfielder grabbed 12 goals from 32 appearances last season.
How did they qualify: Austrian Champions
Champions League pedigree: They have never won the tournament but were runners-up in the UEFA Cup in 1994.
Manager: Felice Mazzu
Most important player: Bryan Heynen. The 22-year-old defensive midfielder could break into the national side this season.
How did they qualify: Belgian First Division A winners
Champions League pedigree: The domestic league trophy last season is the club's first and only major honour.
Manager: Ernesto Valverde
Most important player: Lionel Messi. The rumours are growing that Messi may leave on a free transfer at the end of the season, and what better way to go out than with a Champions League.
How did they qualify: La Liga champions
Champions League pedigree: Barcelona are the team that redefined football and dominated the Champions League as a result.
Manager: Lucien Favre
Most important player: Jadon Sancho. Far from their only talented player, Sancho is on track to become a world class forward and is thriving in Gemany.
How did they qualify: Bundesliga runners-up
Champions League pedigree: Champions in 1997, and they were defeated by rivals Bayern in the final in 2013.
Manager: Antonio Conte
Most important player: Alexis Sanchez. Sanchez was a disaster at Manchester United but is back in Italy where he played some of his best football.
How did they qualify: Fourth in Serie A
Champions League pedigree: They last won with Jose Mourinho in 2010, but Rafael Benitez undid much of his good work and the club is yet to recover.
Manager: Jindrich Trpisovsky
Most important player: Peter Olayinka. The young Nigerian striker has scored goals wherever he has played.
How did they qualify: Czech First League winners
Champions League pedigree: Their greatest European triumph was finishing as runners-up in the Coupe des Nations in 1930.
Manager: Sergei Semak
Most important player: Malcom. He failed to break through at Barcelona but a loan spell in Russia could attract attention from the continent's major clubs.
How did they qualify: Russian Premier League winners
Champions League pedigree: They won the Europa League in 2008, but their best finish in the Champions League has been the round of 16.
Manager: Bruno Lage
Most important player: Ruben Dias. Dias has been linked with a move to the Premier League and is a promising central defender.
How did they qualify: Primeira Liga champions
Champions League pedigree: Benfica are without a European title since Bela Guttmann's infamous curse in 1962 - played eight finals, lost eight finals, including five European Cups
Most important player: Memphis. The ex-Manchester United forward has settled in at Lyon to demonstrate the best of his attacking threat.
How did they qualify: Third in Ligue 1
Champions League pedigree: Champions League, Europa League and Cup Winners' Cup semi-finalists
Manager: Julian Nagelsmann
Most important player: Timo Werner. Perhaps in his last season in Germany after being linked with a move to Liverpool, though he is just one of many promising players at RB.
How did they qualify: Third in the Bundesliga
Champions League pedigree: RB Leipzig's synthetic nature means they have no pedigree in Europe as of yet.
Manager: Frank Lampard
Most important player: Tammy Abraham. Now that the youngsters are in charge, Abraham will be looking to keep his goalscoring form intact on the biggest stage.
How did they qualify: Europa League winners, third in the Premier League.
Champions League pedigree: Chelsea won the Champions League in 2012 and have won two Europa League titles since then.
Manager: Erik ten Hag
Most important player: David Neres. The Brazilian midfielder remained while others left, and with Noussair Mazraoui, Dusan Tadic and Hakim Ziyech still at the club, this is a strong Ajax side.
How did they qualify: Dutch champions
Champions League pedigree: They won the European Cup in 1971, 1972 and 1973, and again in 1995, but could not find their way past Spurs in the semi-finals last season.
Manager: Albert Celades
Most important player: Dani Parejo. In uncertain times for Valencia, the experienced captain will need to be a calming presence for his side.
How did they qualify: Fourth in La Liga
Champions League pedigree: Valencia almost tasted success a little under two decades ago, but were runners-up in 2000 and 2001.
Manager: Christophe Galtier
Most important player: Jonathan Ikone - The young French forward is now an international squad regular and could soon be on the move to a bigger club
How did they qualify: Ligue 1 runners-up
Champions League pedigree: Lille do not have any European pedigree, but they did win the Intertoto Cup in 2004.
*All odds were taken ahead of the first matchday on September 17/18.