The inaugural Guinness Pro14 Rainbow Cup will kick off with three rounds of inter-provincial derbies.
This season's Guinness Pro14 wraps up tomorrow when Munster take on Leinster in the final. The new Rainbow Cup tournament, involving 16 teams - four of which will be from South Africa - then runs from 17 April until 19 June.
The Vodacom Bulls, Emirates Lions; Cell C Sharks and DHL Stormers are the non-European teams taking part.
In Round 1, Ulster host Connacht and Leinster and Munster square up again at the RDS. Two weeks later Leinster head to Connacht with Ulster travelling to Munster, and seven days after that Munster host the Westerners while Leinster welcome Ulster.
A total of six rounds will take place with all teams ranked in a single league table. The top two teams will then play each other in the Guinness Pro14 Rainbow Cup final on 19 June.
Elsewhere, France require a 21 point win and a bonus point against Scotland to win the Six Nations tonight.
Kick off at the Stade de France is at 8.