The two teams meet in Dublin on Friday night
The Republic of Ireland face Wales in a crucial 2018 World Cup qualifier on Friday evening.
It's the first time the teams have met in the qualifying campaign, with the return match to take place later this year in Cardiff.
Martin O'Neill's side currently have a four-point advantage over Wales after four games and they top Group D. That could increase to seven if the home team in Dublin.
Ahead of the game, we have gotten Newstalk Sport's brainiest boffins together, to ask you about the rivalry and the two nations.
Let us know on twitter @NewstalkSport how you get on. Roy Keane will be dishing out the marks at the end of the quiz.
Best of luck!