Llanelli Scarlets travel across the Irish sea to face Ulster in the clash of the weekend. Gareth Jenkins has been forced into nine changes with injuries and the loss of key players to the Wales Six Nations squad.
The Scarlets are just one point ahead of Ulster, so the winner of this tie can steal a march on their closest rival. Ulster collected the Celtic Cup when they beat Edinburgh on December 20, but bowed out of the Heineken Cup last weekend, so are focused on capturing the 'Celtic Double'.
The Warriors will also cross the Irish sea when they play Connacht. Connacht have progressed the semi-finals of the Parker Pen Challenge Cup, while the Warriors narrowly missed out on a place in the final eight of the Heineken Cup. This promises to be a fact paced match between two high quality sides who are battling it out in mid-table.
Leinster make the reverse journey over the Irish sea as they have a match against mike Ruddock's Dragons. With both sides eliminated form the Heineken Cup, and still in contention for the Celtic League crown, much hangs on this match. BBC Wales and TG4 will be covering this game live.
To read team news on the Celtic League website, click here
The Ospreys will be looking to build on their recent victory over Leeds when they play host to Glasgow tonight. In a season that promised much, Lyn Jones will be hoping his side's results turn around, currently in ninth place in the table, it is a position nobody expected when Neath finished runners-up to Munster in the Celtic league last season.
Cardiff Blues have a difficult journey north to face Edinburgh. The Blues are currently in tenth spot, with just 14 points from ten games played, while Edinburgh - Celtic Cup runners-up - are buoyed by being the first Scottish side to make it to the Heineken Cup quarter-finals.