Reigning PRO12 champions Scarlets line out in Pool 5 alongside three-time European Cup winners Toulon, Premiership side Bath and Italy's Benetton.
Teams: Scarlets, Toulon, Bath, Benetton Rugby
For the second season in succession Scarlets and Toulon will meet in the pool stages, while Bath and Benetton make their Champions Cup returns after both missed out last year.
Scarlets
Champions Cup record: P135 W62 D3 L70
Best finish: Semi-final (1999/00, 2006/07)
What's hot: Scarlets head into the new European season as defending league champions having played some breathtaking attacking rugby. Steff Evans, Rhys Patchell, Jon Davies and new signing Leigh Halfpenny are all playing well, while at the breakdown the likes of Tadhg Beirne and John Barclay cause havoc. Wayne Pivac's men are capable of tries from anywhere.
What's not: James Davies' shoulder injury is a huge blow, with his breakdown work up there with the best in Europe, while the losses of Lion Liam Williams to Saracens and DTH Van der Merwe to Newcastle Falcons are bound to be keenly felt.
What's changed: Can they replicate their league displays of last season and earn a first European quarter-final place since 2007? In terms of transfers, the headline changes are the departures of Williams and Van der Merwe, while Wales internationals Halfpenny and Tom Prydie and Australian Sevens international Paul Asquith are among the new arrivals.
Key player: Tadhg Beirne
Toulon
Champions Cup record: P48 W36 D0 L12
Best finish: Champions (2012/13, 2013/14, 2014/15)
What's hot: The embarrassment of riches at their disposal. Already a squad of supremely talented players, Toulon have added the likes of Chris Ashton, Malakai Fekitoa, Facundo Isa, JP Pietersen and Hugo Bonneval among more. All are extremely talented recruits. In terms of experience and pedigree, there are few teams to match Toulon and one would think they are in a good position to top this pool.
What's not: While stars have arrived, others have also exited. The talent of Liam Gill and Leigh Halfpenny left against the wishes of the supporters, while the Ben Barba experiment proved a failure. Club legends Matt Giteau, Drew Mitchell and Juan Smith all also called time on their Toulon careers. The pressure placed on the squad by volatile owner Mourad Boudjellal to succeed can also prove a negative.
What's changed: Fabien Galthie has taken over as the new head coach, while numerous players have arrived and left. Indeed there has been a staggering turnover of 29 players: 12 incoming, 17 outgoing, as is customary Toulon. League convert Semi Radradra has arrived and is starting to rip up a few trees.
Key player: Guilhem Guirado
Bath
Champions Cup record: P59 W48 D0 L11
Best finish: Champions (1997/98)
What's hot: In the backs, the likes of Anthony Watson, Semesa Rokoduguni, Matt Banahan and Jonathan Joseph mean Bath have some of the best talent on display. A potential back-row of Francois Louw, Sam Underhill and Taulupe Faletau also has the capacity to be devastating.
What's not: The loss of influential playmaker George Ford could prove to have a major affect on Todd Blackadder's side. The club may also regret letting wing Robbie Fruean leave to Edinburgh, particularly if the big Kiwi can stay fit in the Scottish capital. In terms of on the pitch, the scrum would appear to be an area of concern.
What's changed: After a year away from Europe's top table, Bath return for the 2017/18 season. The signing of flanker Underhill from Ospreys looks like one of the most impressive in Europe, while Rhys Priestland has so far adapted well to being the No 1 fly-half in Ford's absence. Consistency from him and Freddie Burns is paramount to their success.
Key player: Anthony Watson
Benetton Rugby
Champions Cup record: P108 W19 D1 L88
Best finish: Pool Stages
What's hot: For the first time in a long time, Benetton head into Europe off the back of a good run of form. Three wins from their last four games, including impressive wins at Edinburgh and over Ospreys have given the club some much-needed confidence. The signings of fly-half Marty Banks from the Highlanders and Maori All Black Whetu Douglas from the Crusaders look positive.
What's not: Losing international pair Luke McLean and Filo Paulo to London Irish is a negative, while the club have consistently struggled in the PRO12 and Europe for some time. In fact from their last three Champions Cup campaigns they have lost 17 games and won just once. Will they be up to the task defensively against such talented opposition?
What's changed: Benetton are back in the Champions Cup for 2017/18, having finished above Zebre in last year's table. The format for European qualification has changed from this season, however, and to earn a place in next year's European Cup they will have to finish in the top four of PRO14 Conference B, or lower depending on if the Kings (illegible for European competition) finish above them. Either way, an improvement is necessary if they want to continue competing at Europe's top table.
Key player: Ian McKinley