Alan Quinlan: Nobody will play their way onto the plane but they could play their way off it
There are probably 23 spots already nailed down in Ireland's World Cup squad. That means the other 23 players in the squad are now battling for the remaining eight places.
That battle begins in earnest today in Cardiff. Some lads will have been putting their hands up in training, maybe posting big fitness scores, but what really matters is what happens on the pitch in a match situation and that's what we will begin to see today.
Lads will have been itching to get this chance and it is a huge game for so many players. They may not get another opportunity, and given that none of them have been in a match situation for a few months, that makes it all the more difficult.
I was not surprised to hear Joe Schmidt say that he will probably go with a 17-14 split in terms of forwards and backs.
That's the most logical position but, as always, it is only when you start breaking it down that you realise just how many tough calls have to be made.
I think they will bring three out-halves to the World Cup - Ian Madigan will cover centre as well - and three scrum-halves, so that leaves just eight places for all the other backs.
Indeed, the battle for those eight spots to cover full-back, the wings and the centres will probably be the most competitive area of selection.
It will probably be the one area which will lead to the most disappointment as well. There will be some guys there who will feel confident of selection but will end up not making the cut and, naturally, it will be very hard to take.
In these situations, versatility gives players an edge, and that's why today is such a big occasion for Keith Earls. It's hard to believe he has never played under Schmidt - Donnacha Ryan the same - and his selection today at 13 is interesting.
Like Donnacha, he has had to battle so much to recover from injury and he is trying to get back into a side which has just won back-to-back Six Nations crowns.
It's a big chance for him. He needs to show the physicality and carry the ball and he really needs to show an edge today. We all know how Schmidt demands intensity and accuracy and that's what he will be watching for.
I reckon Ireland will go with two full-backs, three centres and three wingers, so a player who can cover more than one of those positions has an advantage if he is performing.
It's a big day as well for Darren Cave, same for Fergus McFadden, and Andrew Trimble will be bursting to show he has the form which made him such a key part of the 2014 Six Nations success.
Schmidt has stated that some will be cut from the group without getting a chance on the field, so these guys know this could be their only chance.
Paddy Jackson has seen off Ian Keatley for the third out-half spot and he will now be turning his attention to closing the gap on Madigan and pushing for that place on the bench. He has played really well for Ulster and has put that poor debut against Scotland behind him.
The make-up of the pack will be just as interesting. I suppose a lot will depend on how Cian Healy progresses and how vital it might be to bring a back-up prop who can cover both sides.
I reckon we are looking at two looseheads, three tightheads and three hookers, so the battle here is really for the prop positions.
Jack McGrath will be keen to show that he can again fill in for Healy, while Dave Kilcoyne will relish a chance off the bench to show he is primed.
Ryan, like Iain Henderson, can move from second-row to back-row and that again is the sort of versatility which is worth an awful lot when you are bringing a squad to a World Cup.
He has had to wait a long time for this chance but he showed when Paul O'Connell was out for Munster that he can run a lineout, and Schmidt will have to consider what to do if Paulie gets injured during the tournament. It's great to see him back, he's a quality player.
I think it is fairly safe to say that the starting back-row will be Peter O'Mahony, Seán O'Brien and Jamie Heaslip. The battle is for the back-up spots.
It is probably a straight fight between Tommy O'Donnell and Chris Henry for the back-up seven. Tommy needs to make the most of this opportunity as Chris has been a starter under Schmidt and is a quality player.
The fact that the match sold out in the Millennium Stadium so quickly suggests that supporters know there is a huge amount at stake, even though they know the rugby will probably be rusty given that players have not been in action for so long.
It's been interesting as well the way both sides have approached this game in such contrasting fashions.
Ireland have been low-key, they have stayed in Carton House for their preparations aside from a couple of camps in Galway and Cork, and players have been returning home and to their provinces.
There hasn't really been a huge amount about them.
Wales, in contrast, come into this having spent a couple of weeks in high-altitude training in Switzerland and a week in intense heat in Qatar.
In addition, Warren Gatland has been talking up their preparations an awful lot, saying how good things are going and so on.
I have no doubt it is a bit of a ploy - there is always method in his madness, although I'm not sure where he is going with this one!
The approach is in stark contrast to Ireland but they have every bit as much to play for today and while I wouldn't expect the rugby to be great, it will be a fascinating contest.
I suppose it is safe to say that no-one will book their place on the plane today, but a lad could play his way out of the squad.
With that riding on it in a packed stadium with the roof closed, it will whet the appetite for real stuff in the next month, and all the twists and turns which will undoubtedly happen.
In a way, the World Cup kicks off today.