European Champions Cup - pool-by-pool guide
In the past five years, the European Champions Cup has been under a duopoly.
Saracens have won the past two titles, successfully defending the trophy in May with victory over Clermont.
Before that, big-spending French superpowers Toulon won an unprecedented three in a row between 2012 and 2015.
But a new season brings new contenders.
Might the new money of Montpellier - under the guidance of former Scotland coach Vern Cotter - sweep to the top of the European game?
Meanwhile, English champions Exeter are turning their sights to a continental challenge, and the twin Irish threat of Leinster and Munster will want to go at least one better than last season's semi-final defeats.
Or could Scarlets land the trophy for the first time for Wales on the back of a thrilling Pro12 triumph in May?
It will be a long, entertaining and intriguing road to the final in Bilbao on 12 May.
|Champions Cup opening-round coverage|
|Listen to 5 live Rugby Union Weekly's full preview of the tournament|
|Friday 19:00 BST, 5 live sports extra & Radio Ulster:||Ulster v Wasps|
|Saturday 14:50 BST, 5 live sports extra||Racing 92 v Leicester|
|Saturday 17:15 BST, 5 live sports extra||Harlequins v La Rochelle|
|Saturday 19:30 BST, 5 live sports extra||Exeter v Glasgow|
|Sunday 15:10 BST, 5 live sports extra & Radio Wales||Toulon v Scarlets|
|Sunday 17:15 BST, 5 live sports extra||Northampton v Saracens|
|Sunday 17:30 BST, BBC Radio Wales||Ospreys v Clermont|
Pool 1: Harlequins, Ulster, La Rochelle, Wasps
The Champions Cup is a formidable competition whoever you are, wherever you come from and whatever your pedigree.
And this group typifies how open and unpredictable it can be.
On their best form, all of the teams in Pool 1 are going to fancy their chances.
La Rochelle are a coming force in France.
They finished top of the Top 14 in the regular season last campaign and have won five out of seven at the start of this.
A lot will depend on whether they fight on two fronts or instead choose to focus their resources on winning their domestic title, which carries greater cache in France.
Wasps are starting to really exert themselves in continental competition, building on campaigns year after year, just as Saracens did successfully in the run-up to their first European title in 2016.
But if they are to better last season's run to the final eight, they will have to overcome a rotten run of injuries that left them without 15 players - including fly-half Danny Cipriani - at the beginning of this month, and an indifferent start to this campaign.
Ulster have been quiet in Europe for the past few seasons after that run to the 2012 final, but are under a new coach in Jono Gibbes, who won this tournament three times in his time on Leinster's backroom staff and has more recently been involved in Clermont's assault on the business end of the Champions Cup.
Player to watch: Marcus Smith (Harlequins)
After he was promoted to England's senior training squad earlier this year, there is understandably a lot of excitement around 18-year-old Marcus Smith.
Having made the step up to the Quins first team so early and promisingly, it will be interesting to see what he can do at this higher level of competition.
He is small for a modern fly-half but he doesn't go missing at all in defence. Attacking-wise, he has a very complete skillset. He has great vision, great hands, pace, a step and a nose for a gap - he's an all-round threat.
Pool 2: Clermont, Northampton, Ospreys, Saracens
Since losing to that sensational Leinster rally in the 2011 final, Northampton keep threatening to mount a European campaign without managing to deliver on the pitch.
Even with the totemic French number eight Louis Picamoles at Franklin's Gardens last season, they finished bottom of Pool 4. And they are missing his cannonball runs this time around after Montpellier tempted him back home.
All in all it is difficult seeing either Saints or Ospreys getting much change from Clermont and Saracens, who contested last year's final.
Who tops the pool might well come down to who travels better and the December double-header when Clermont and Saracens meet on successive weekends will be a seismic couple of matches.
Player to watch: Piers Francis (Northampton)
The Northampton centre was playing for the Auckland Blues last season - but missed the New Zealand franchise's match against the British and Irish Lions to accept a call-up to England's tour of Argentina.
He has experience of playing in Super 14 and should flourish with the new rules that mean the ball is in hand for longer.
He is not an enormous fellow or particularly rapid, but is an astute all-round footballer.
As a former fly-half, I wonder if Saints are looking at a double playmaking axis with him and Stephen Myler or Harry Mallinder.
Pool 3: Exeter, Glasgow, Leinster, Montpellier
This is another really tough group.
Montpellier are right up the top end of the French Top 14, have a new coach in Cotter and a mouth-watering eight-nine-10 axis of Picamoles, former Ulster scrum-half Ruan Pienaar and former All Black Aaron Cruden.
Leinster have huge and relatively recent European pedigree having lifted the trophy in 2009, 2011 and 2012. This tournament inspires something special in them and the likes of fly-half Jonny Sexton and prop Cian Healy will want one last hurrah as they approach the end of their careers. On their day they can play some amazing rugby.
Exeter Chiefs - crowned Premiership champions for the first time earlier this year - will have their credentials really tested at this higher level.
Glasgow have been improving every year under Gregor Townsend and, now he has headed off to the Scotland job, they have made a smart appointment to build on those foundations in Dave Rennie, who took the Chiefs to back-to-back Super Rugby titles in 2012 and 2013.
They will be underdogs but, after reaching the quarter-finals last season and opening this season with six straight wins in Pro14, perhaps they shouldn't be.
Player to watch: Sam Simmonds (Exeter)
The 22-year-old number eight is from a different mould when compared to some of his rivals for an England spot - players such as Billy Vunipola and Nathan Hughes.
He is smaller, less physical in close quarters, but he is quicker, makes breaks and scores tries.
He is almost the build of a modern-day centre, but that pace and the ability to offer a line-out option is a real point of difference in a modern back row. His speed is a real asset in defence as well, as he gets to the breakdown and disrupts.
Pool 4: Castres, Leicester, Munster, Racing 92
It is a tough call to say who will come out of this one, with Leicester, Munster and Racing all competing for top slot.
When New Zealand's two-time World Cup-winning fly-half Dan Carter first arrived in Paris in 2015, Racing seemed like an unstoppable, insatiable force.
They have some superb training facilities and are due to move into their brand-new U Arena in December, but they don't seem to have kicked on since their 2016 campaign, when they came within a match of a superb double, winning the French title but losing to Saracens in the final of the Champions Cup.
Perhaps it was the doping charges brought, and subsequently dismissed, against two of their biggest stars or the possibility of them being merged with Stade Francais, but they finished bottom of their group in the Champions Cup and sixth in the Top 14 last season.
Leicester are improving and getting used to each other after a raft of changes over the summer. They have a serious attacking backline, with new signings George Ford and Jonny May adding new threat. but their forwards will be under pressure against the heft of a group that contains two beefy French forward units.
Munster were inspired in the wake of coach Anthony Foley's death last season and it was incredible to see the club, community and players come together in the way they did. Whether they can sustain that momentum this season is difficult to know.
Player to watch: Ellis Genge (Leicester)
A former back-row-turned-prop, Ellis Genge is an aggressive, direct ball-carrier. He makes a decision quickly and acts at the same speed. If he can find a hole, he is going through it. If he can't, he is dead set on winning the collision.
He is 22, a spiky competitor, and sometimes that enthusiasm overspills a little.
But he can keep it under control, otherwise he wouldn't be in the team.
Pool 5: Benetton, Bath, Scarlets, Toulon
Pool Five is the lucky pool.
Being grouped with an Italian team means the other three should take bonus-point victories home and away against Benetton.
That is a 10-point head-start.
The three runners-up who qualify for the last eight usually have about 19 or above. The teams in Pool 5 are already halfway there if they do what they should do.
Toulon have a pack that basically precludes taking them on up front. It is a waste of time to try and grind them down up front. It is a cul-de-sac of a tactic.
They don't play fast and wide like they used to with Jonny Wilkinson at fly-half.
Scarlets would be my dark horses. They have some serious talent with centre Jonathan Davies, British Lions man of the series in New Zealand, ably supported by the likes of full-back Leigh Halfpenny, scrum-half Gareth Davies and wing Steff Evans.
Losing Liam Williams to Saracens in the summer is a big loss, but after winning the Pro12 last season they should have massive belief that they can do something in the competition.
Bath's front five probably is not heavy duty enough, but if they can take something from Parc y Scarlets in the second game then they could be in the mix. That could be the crucial game for them.
Player to watch: Taulupe Faletau (Bath)
The Wales number eight's stock in world rugby just keeps going up and up.
It is a mark of really high-quality player, when you are playing in a team like Bath, who are not dominating up front, playing a defensive pattern quite a lot of the time, and still impress.
Jeremy Guscott was speaking to BBC Sport's Mike Henson.