It's part two of the opening block of European games with three Irish provinces in action in the Investec Champions Cup, and one in the Challenge Cup this weekend.
Munster, big winners over Stade Francais in round one, are in Castres on Friday night in Pool 3, while Ulster have a Saturday afternoon date with Bordeaux Begles in Belfast as they bid to bounce back from a heavy loss at Toulouse.
Leinster are looking to start with back-to-back victories after Sunday's win at Bristol when they host Clermont Auvergne in Dublin later on Saturday.
Meanwhile, Connacht, who began their Challenge Cup campaign with victory over Zebre Parma, face Perpignan on Sunday.
Find out all you need to know about the weekend's games here.
ONLINE
We'll have live updates, live scoring, reports and reaction from all games on rte.ie/sport.
TV
You can watch live coverage of Leinster v Clermont (Saturday 5.30pm) on RTÉ2 and RTÉ Player. Castres v Munster (Friday 8pm) and Ulster v Bordeaux (Saturday 3.15pm) are live on Premier Sports. Perpignan v Connacht (Sunday 1pm) is also on Premier Sports.
RADIO
There will be live commentary of Ulster v Bordeaux on Saturday Sport on RTÉ Radio 1.
WEATHER
Castres in the south of France is set for light clouds and wind in about 6C this evening.
On Saturday, Ulster should get under way with light cloud and a gentle breeze in Belfast, temperatures are forecast for about 6C.
Rain should stay away from Dublin for Leinster's game on Saturday evening, it will be partly cloudy with a gentle breeze in about 5C.
It's sunny intervals in a fresh breeze for Connacht in Perpignan on Sunday afternoon where temperatures are predicted around 9C.
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Ian Costello's Munster are the first of the Irish clubs in action as they face a trip to Castres in Pool 3.
The visitors recorded a fine 33-7 win over an ill-disciplined Stade Francais last weekend, while Castres, under former Ulster, Ireland and Lions lock Jeremy Davidson, took a 38-8 beating at Northampton.
Munster were one of three teams last weekend who didn’t lose a single scrum or lineout.
It's the 19th ever meeting between the teams with tonight's visitors having 13 wins, a draw and four defeats to their name.
They have changed six players from the side that beat Stade, including returning captain Tadhg Beirne to the starting line-up.
The French side are currently in seventh place in the Top14.
Castres: Julien Dumora; Geoffrey Palis, Jack Goodhue, Andrea Cocagi, Rémy Baget; Louis le Brun, Jeremy Fernandez; Quentin Walcker, Gaetan Barlot, Will Collier; Gauthier Maravat, Leone Nakarawa; Mathieu Babillot (capt), Tyler Ardron, Abraham Papalii.
Replacements: Loris Zarantonello, Wayan de Benedittis, Nicolas Corato, Paul Jedrasiak, Feibyan Tukino,Santiago Arata Perrone, Theo Chabouni, Adrien Seguret.
Munster: Mike Haley; Calvin Nash, Tom Farrell, Alex Nankivell, Thaakir Abrahams; Jack Crowley, Craig Casey; Dian Bleuler, Niall Scannell, Stephen Archer; Fineen Wycherley, Tadhg Beirne (capt); Peter O'Mahony, John Hodnett, Brian Gleeson.
Replacements: Diarmuid Barron, Dave Kilcoyne, Oli Jager, Tom Ahern, Alex Kendellen, Paddy Patterson, Rory Scannell, Jack O'Donoghue.
Referee: Christophe Ridley (Eng)
Ulster shipped a record number of points last weekend at Toulouse, going down 61-21 at Stade Ernest Wallon.
After leaving returning internationals Rob Herring, Iain Henderson, Tom O'Toole and Cormac Izuchukwu on the bench, it seemed a team picked with Bordeaux in mind, but boss Richie Murphy will still have been disappointed not to get a fourth try and a bonus point.
Bordeaux, who reached the quarter-finals last season, overcame a slow start against Leicester in round one before running out 42-28 winners.
The French outfit, under head coach Yannick Bru, are second in the Top14.
Bordeaux's last visit to Belfast was seven years ago, when they won 22-26.
Robert Baloucoune (calf), Jake Flannery (ankle), Jacob Stockdale (hamstring), Ethan McIlroy (ankle), Sean Reffell (ankle), James Hume (knee), Callum Reid (knee) and Tom Stewart (ankle) are all out with injury.
Former Leinster and Munster out-half Joey Carbery starts for the visitors.
Ulster: Michael Lowry; Werner Kok, Jude Postlethwaite, Stuart McCloskey, Zac Ward; Aidan Morgan, Nathan Doak; Eric O'Sullivan, Rob Herring, Tom O'Toole, Iain Henderson (capt), Kieran Treadwell; Cormac Izuchukwu , Nick Timoney, David McCann.
Replacements: John Andrew, Andrew Warwick, Scott Wilson, Harry Sheridan, Marcus Rea, Dave Shanahan, James Humphreys, Rory Telfer.
Bordeaux: Louis Bielle-Biarrey; Damian Penaud, Nicolas Depoortere, Yoram Moefana, Arthur Retiere; Joey Carbery, Maxime Lucu (capt); Jefferson Poirot, Romain Latterrade, Carlü Sadie; Guido Petti, Jonny Gray; Marko Gazzotti, Lachie Swinton, Tevita Tatafu.
Replacements: Maxime Lamothe, Ugo Boniface, Ben Tameifuna, Adam Coleman, Alexandre Ricard, Bastien Vergnes-Taillefer, Rohan Janse van Rensburg, Matéo Garcia.
Referee: Gianluca Gnecchi (Ita)
Leinster, also slow out of blocks in their opening fixture against Bristol last weekend, came good in the second half to record a 35-12 win at Ashton Gate, thanks in no small part to the impact of replacements RG Snyman and Jordie Barrett.
Leo Cullen's side, beaten finalists for the last three years, have won eight of their eight games so far this season, and have not lost a pool game in this tournament since 2018.
Clermont are third in the Top14 and come into this game off the back of a 28-0 win over Benetton, in which all four tries came from the forwards.
Ireland internationals Tadhg Furlong, Ciarán Frawley, James Lowe and Hugo Keenan are unavailable through injury, while Jordie Barrett gets a first start and Sam Prendergast retains the 10 shirt.
Leinster: Jordie Barrett; Liam Turner, Garry Ringrose, Robbie Henshaw, Jimmy O'Brien; Sam Prendergast, Jamison Gibson-Park; Andrew Porter, Rónan Kelleher, Thomas Clarkson; Joe McCarthy, James Ryan; Max Deegan, Josh van der Flier, Caelan Doris (capt).
Replacements: Gus McCarthy, Cian Healy, Rabah Slimani, RG Snyman, Jack Conan, Fintan Gunne, Ross Byrne, Andrew Osborne.
Clermont: Alex Newsome; Lucas Tauzin, Pierre Fouyssac, George Moala, Alivereti Raka; Irae Simone, Baptiste Jauneau; Etienne Falgoux, Etienne Fourcade, Michael Ala'alatoa; Peceli Yato, Rob Simmons; Killian Tixeront, Alexandre Fischer, Fritz Lee (capt).
Replacements: Barnabe Massa, Giorgi Akhaladze, Cristian Ojovan, Oskar Rixen, Antoine Chalus-Cercy, Sebastien Bezy, Ben Urdapilleta, Theo Giral.
Referee: Luke Pearce (Eng)
Connacht responded to the concession of an early try against Zebre last weekend with a seven-try trouncing of the Italians at Dexcom Stadium.
Chay Mullins scored a hat-trick and Paul Boyle helped himself to a brace in a 43-12 win.
Perpignan, meanwhile, came away from the NRCA Stadium in Amsterdam with a draw against Cheetahs, thanks to a late Antoine Aucagne penalty.
Perpignan: Ali Crossdale; Jefferson Joseph, Riko Buliruarua, Apisai Naqalevu, Maxim Granell; Antoine Aucagne, James Hall; Lorencio Boyer-Gallardo, Seilala Lam (capt), Nemo Roelofse; Alessandro Ortombina, Adrien Warion; Noe Della Schiava, Max Hicks, Andro Dvali.
Replacements: Victor Montgaillard, Johan Barcenilla D'Onghia, Kieran Brookes, Bastien Chinarro, So'otala Fa'aso'o, Gela Aprasidze, Tommaso Allan, Freddy Duguivalu.
Connacht: Santiago Cordero; Chay Mullins, Byron Ralston, Cathal Forde, Andrew Smith; Jack Carty, Matthew Devine; Denis Buckley, Eoin de Buitléar, Sam Illo; Darragh Murray, Joe Joyce; Cian Prendergast (capt), Shamus Hurley-Langton, Seán O'Brien.
Replacements: Adam McBurney, Jordan Duggan, Jack Aungier, Oisín Dowling, Paul Boyle, Ben Murphy, David Hawkshaw, Conor Oliver.
Referee: Sara Cox (Eng)
Elsewhere, the pick of the other weekend games sees La Rochelle host Bristol on Saturday evening, while champions Toulouse are in Exeter late on Sunday.
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