Barcelona begin their quest to become the first club to successfully defend their Champions League title when the Catalan outfit visit Roma in Wednesday's Group E opener.
The Spanish giants beat Juventus in last season's final and are coming off a season that saw them clinch a Primera Division, Copa del Rey and Champions League treble.
"We are the champions and we will try to make history by winning the Champions League in successive seasons," Barcelona head coach Luis Enrique said, according to Spanish sports daily Marca.
The feat was achieved by multiple clubs during the days of the competition's predecessor, the European Cup, but since the Champions League launch in 1992-93 no side has managed back-to-back titles.
Luis Enrique will be facing one of his former clubs, while Lionel Messi will make his 100th Champions League appearance at the Stadio Olimpico.
Also in Group E, Germany's Bayer Leverkusen will host BATE of Belarus at the BayArena.
The Bundesliga side have advanced to the last 16 in each of their six attempts.
Chelsea have won just one of their six matches in all competitions and square off against Maccabi Tel Aviv in their Group G opener at Stamford Bridge.
Last season's Barclays Premier League champions have yet to win at home this campaign.
Porto travel to Ukraine to face Dynamo Kiev in their Group G opener.
The Portuguese club have not lost on their previous six visits to Ukraine.
Dinamo Zagreb are back in the group stages for the first time since 2012 and will be looking to end a 15-match winless run in the competition when Arsenal visit the Croatian club in their Group F showdown.
Also in Group F, Bayern Munich start their European campaign with an away trip to Olympiacos.
The Bundesliga champions reached the semi-finals of the competition for the fourth time in a row last season.
Valencia, back in Europe's top competition after a two-year absence, are at home against Zenit St Petersburg in Group H.
Also in their pool are Gent, who are playing for the first time in the group stages.
The Belgian club host a Lyon side who last played in the competition in the 2011-12 campaign.
