But, with just a few days to go until the Pro12 spectacle gets under way, just how good is your knowledge of Welsh rugby, anyway?
BBC Wales Sport presents the ultimate regional quiz ahead of the fifth Judgement Day in the Welsh capital.
Do you know your Steve Shingler from your Aaron Shingler? What about your Lloyd Williams from your Tom Williams?
Ahead of Judgement Day this Saturday, test your regional knowledge with this BBC Wales Sport quiz.
(Photo credit: Huw Evans Picture Agency)
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Judgement Day is soon upon us and once again, the four Welsh regions - Ospreys, Scarlets, Cardiff Blues and Newport Gwent Dragons - will play two games on the hallowed Principality Stadium turf.