Manchester City's new coach Pep Guardiola will be heading back to Barcelona after the Premier League club was pitted against his former team in the Champions League draw on Thursday.
Guardiola, who also spent most of his playing career at the Catalan club, steered Barcelona to two Champions League titles as well as a number of other trophies during his time as coach from 2008-12.
The two teams play each other on 19 October in Barcelona and 1 November in Manchester.
Borussia Moenchengladbach and Celtic complete Group C.
Cristiano Ronaldo also returns to his first club as holder Real Madrid has been drawn against Sporting Lisbon. Borussia Dortmund and Legia Warsaw are also in Group F.
Surprise Premier League champion Leicester City faces Porto, Brugge and FC Copenhagen in its first time in Europe's premier competition.
The eight four-team groups begin play on 13-14 September.
Paris Saint-Germain and Arsenal will be favorites to progress but Basel boasts a fearsome record against English clubs in European competition.
Neither team has ever won the European Cup but PSG reached the quarterfinals in the last four seasons. However, it is now without Swedish star Zlatan Ibrahimovic, who moved to Manchester United in the off season.
Arsenal was eliminated in the round of 16 in the last six seasons.
Since 2011, Basel has helped eliminate Manchester United and Liverpool from the Champions League, as well as knocking Tottenham out of the Europa League.
Ludogorets is playing in the group stages for only the second time in the Bulgarian club's history, having reached the same stage two years ago.
Napoli will be hoping for better luck than the last time they reached the group stages.
In 2013/14, Napoli became the first — and so far only — team to fail to progress after picking up 12 points, losing out to Dortmund and Arsenal in a three-way head-to-head.
It should have an easier time this campaign, as it has been pitted against Benfica, Dynamo Kiev and Besiktas.
While Guardiola will be highly familiar with Barcelona, many of City's players will also know the Catalan club well.
Barcelona beat City at the last-16 stage in 2014 and 2015, while goalkeeper Claudio Bravo has just completed a move from the Spanish champion to Guardiola's new side.
"It's good for Pep because he knows Borussia very well from his time at Bayern and Barcelona as well so we will see," City's Director of Football Txiki Begiristain said.
"He had been back to Barca before with Bayern Munich so it's not the first time he's been returned to the Camp Nou. Barcelona will start as favorites for the group but that is nothing new, they are a fantastic side."
City also played Moenchengladbach in the group stage last year en route to the semifinals.
Celtic will be hoping for a repeat of the 2012-13 season when it managed a shock 2-1 home win over Barcelona 2-1 in the group stage.
Bayern Munich will be out for revenge when it faces Atletico Madrid after losing to the Spanish side on away goals in last season's semifinals.
In May, Atletico lost the final on penalties to Real Madrid — finishing runner-up to its bitter rival for the second time in three years.
Contrasting sides in PSV Eindhoven and Rostov make up the group.
PSV has played regularly in European competition since the 1970s, while it is Russian side Rostov's maiden appearance in the European Cup.
A group where anyone could win it or finish bottom.
None of the teams have ever won the competition although Leverkusen and Monaco have both reached the final — in 2002 and 2004 respectively.
Tottenham last played in the Champions League in 2010-11, reaching the quarterfinals, while CSKA Moscow made a group stage exit in 2013-14.
Matches between Real Madrid and Borussia Dortmund are swift becoming classics.
Madrid beat Dortmund in the quarterfinals in 2014, avenging its semifinal defeat the previous campaign.
No team has successfully defended the Champions League since its inception in 1992 but Madrid forward Gareth Bale hopes his side can become the first to do so, with the final being staged in his home city of Cardiff.
"It would be amazing to experience a Champions League final in Cardiff," Bale said. "It is obviously a difficult group but it always is in the Champions League. We fancy our chances to get through but we know there are going to be some difficult games."
Meanwhile, as well as providing a former player in Ronaldo, Sporting had more players than any other club in Portugal's Euro 2016-winning squad — Rui Patrício, Joao Mario, William Carvalho and Adrien Silva.
Legia Warsaw completes the group, becoming Poland's first team in the Champions League proper in 20 years.
Apart from two-time winner Porto, Group G is devoid of Champions League pedigree.
Leicester, which was in the third tier of English football in 2009, is making its debut in the competition.
Copenhagen reached the last 16 in 2010/11, one of only four previous times it has made it into the Champions League proper, while Brugge has also had only sporadic appearances in the group stages.
Juventus and Sevilla face each other in the group stages for the second successive season.
Juventus beat Sevilla 2-0 at home but lost 1-0 in Spain, which meant it finished second in the group and faced Bayern Munich in the last 16 rather than Dinamo Kiev. The Turin side lost after extra time in the second leg in Germany.
"We missed an opportunity at Sevilla last year," Juventus coach Massimiliano Allegri wrote on Twitter. "It will be a red-hot atmosphere in Lyon and Zagreb: we need to be focused, we know our aim."
Sevilla was eliminated from the Champions League and went on to win the Europa League for the third season in a row.
Lyon completes the group along with Dinamo Zagreb, which established one of the worst records in a group stage campaign, having lost all six games with a goal difference of minus 19 in 2011.