Here's a quick look at the sides:
Coach: David Young
Captain: Rhys Williams
Pool rivals: Calvisano, Leeds Tykes, Perpignan.
Key signings: Andy Powell (Scarlets), Mike Phillips (Scarlets), Xavier Rush (Auckland), Marc Stcherbina (Northampton), Jonah Lomu (New Zealand)
Key losses: Andrew Lewis, Richard Smith, Nick Walne (all retired), Freddie Tuilagi (released), Johnny Vaughton (Ospreys), Nathan Thomas (Leeds Tykes)
Players to watch: MIKE PHILLIPS: Making a real claim for the Wales No 9 jersey in the wake of Dwayne Peel's ankle problems. A powerful player who acts as a fourth backrower. XAVIER RUSH: Quality off-season purchase who brings much-needed experience and leadership to the Arms Park side.
Coach: Gareth Jenkins
Captain: Simon Easterby
Pool rivals: Edinburgh Gunners, London Wasps, Toulouse
Key signings: Regan King (Stade Francais), Dafydd James (Harlequins), Inoke Afeaki (Secom, Japan), Alix Popham (Leeds Tykes), Clive Stuart-Smith (Worcester), Mike Hercus (Sale Sharks), Hottie Louw (Clermont Ferrand)
Key losses: Andy Powell (Blues), Arwel Thomas (Neath), Salesi Finau (Bath), Aisea Havili (Worcester), Scott Quinnell (retired), Mike Phillips (Blues), Ian Boobyer (Maesteg), Mark Taylor (Sale Sharks), David Hodges (retired), Jon Thiel (Canada), Leigh Davies (Ospreys)
Players to watch: LEE BYRNE: The surprise package of the early-season matches whose damaging runs from the back are making him a crowd favourite at Stradey Park. SIMON EASTERBY: The hard-working Irishman is one of the few players to return from the British Lions tour with his head held high, and he will lead from the front all season.
NEWPORT GWENT DRAGONS
Coach: Paul Turner
Captain: Jason Forster
Pool rivals: Castres Olympique, Munster, Sale Sharks
Key signings: Andrew Hall (Glasgow), Leigh Hinton (Bedford)
Key losses: Rod Snow (retired), Percy Montgomery (Natal Sharks), James Richards (NEC Harlequins)
Players to watch: MICHAEL OWEN: Will be feeling the pressure from Ryan Jones and Colin Charvis to keep his Wales spot and will produce some inspirational performances for the Dragons. KEVIN MORGAN: One of the most dangerous attackers in the game who just needs an injury-free run of games to show his best form.
Coach: Lyn Jones
Captain: Barry Williams
Pool rivals: Clermont Auvergne, Leicester Tigers, Stade Francais Paris
Key signings: Johnny Vaughton (Blues), Leigh Davies (Scarlets), Alun Wyn Jones (Swansea), Damian Karauna (New Zealand), Adrian Cashmore (New Zealand)
Key losses: Luke Tait (Canada), Nathan Bonner-Evans (Sale Sharks), Adrian Durston (Viadana), David Tiueti (Coventry), Elvis Seveali'i (Sale Sharks)
Players to watch: ADRIAN CASHMORE: Would have earned a sack-full of caps for New Zealand if it wasn't for some bloke called Christian Cullen. Quality player and talented goal-kicker. DUNCAN JONES: Unlucky to miss the British Lions tour, but has the talent and experience to force his way back into Test selection.
First round draw (UK times):
Saturday: Blues v Leeds Tykes (1pm), Toulouse v Scarlets (3pm), Castres Olympique v Dragons (5.15pm)
Sunday: Ospreys v Stade Francais (3pm)