La Celtic League, rebaptisée Magners League du nom du sponsor principal de l'épreuve, est un championnat opposant les quatre provinces irlandaises, quatre franchises galloises et deux villes écossaises.

CARDIFF BLUES
Pays de Galles
Fondation: 2003
Stade: Arms Park (Cardiff, 13.000 places)
Manager: David Young; Capitaine: Paul Tito

CONNACHT RUGBY
Irlande
Fondation: 1885
Stade: Sportsground (Galway, 5.000 places)
Manager: Michael Bradley; Capitaine: John Muldoon

EDINBURGH
Ecosse
Fondation: 1970
Stade: Murrayfield (Edimbourg, 67.500 places)
Manager: Andy Robinson; Capitaine: Mike Blair

GLASGOW WARRIORS
Ecosse
Fondation: 2000
Stade: Firhill Arena (Glasgow, 10.900 places); Hughenden (Glasgow; 6.000 places)
Manager: Sean Lineen; Capitaine: Alastair Kellock

LEINSTER RUGBY
Irlande
Fondation: 1879
Stade: Royal Dublin Society (Dublin, 18.500 places)
Manager: Michael Cheika; Capitaine: Leo Cullen

MUNSTER RUGBY
Irlande
Fondation: 1879
Stade: Thomond Park (Limerick, 26.500 places); Musgrave Park (Cork, 8.000 places)
Manager: Tony McGahan; Capitaine: Paul O'Connell

NEWPORT GWENT DRAGONS
Pays de Galles
Fondation: 2003
Stade: Rodney Parade (Newport, 11.700 places)
Manager: Paul Turner; Capitaine: Tom Willis

OSPREYS
Pays de Galles
Fondation: 2003
Stade: Liberty Stadium (Swansea, 20.500 places)
Manager: Sean Holley; Capitaine: Ryan Jones

SCARLETS
Pays de Galles
Fondation: 2003
Stade: Stradey Park (Llanelli, 10.800 places)
Manager: Nigel Davies; Capitaine: Simon Easterby

ULSTER RUGBY
Irlande
Fondation: 1879
Stade: Ravenhill Park (Belfast, 12.000 places)
Manager: Matt Williams; Capitaine: Rory Best