There have been Six Nations deciders, World Cup nail-biters and once-off games against the world's best, but there is an argument to be made that this is the most important fixture of Joe Schmidt's tenure as Ireland coach.
or the first three seasons at the helm, the New Zealander could do no wrong and even when his team - diminished by injury - exited the World Cup meekly there was a standing ovation for him on The Late, Late Show.
Fast-forward 18 months and the firm ground on which Schmidt once stood is no longer rock solid.
His position is not in question - he will be Ireland's coach at the next World Cup in Japan - but his tactics and selection are coming in for more scrutiny than ever, and if Ireland finish with a defeat on home soil to a record-breaking England side celebrating back-to-back Grand Slams, there will be a definitive indicator that his team is on a downward trajectory.
Four months ago, Schmidt was on top of the world after defeating New Zealand in Chicago, but away defeats to Scotland and Wales have diminished his side's standing.
Defeat today would see Ireland finish the Championship with a negative record for the first time in Schmidt's time in charge.
Depending on results, Ireland could place anywhere from second to fifth at the end of today's proceedings, and there is the added pressure of the World Cup pool draw taking place in May, with Ireland fighting to preserve their place alongside England, New Zealand and Australia as top seeds.
If Wales win and Ireland lose, they swap places in the rankings, and Schmidt's men will be swimming with the sharks.
For their opponents, the equation is simple. Eddie Jones' team will finish first in the Six Nations table regardless of whether they win, lose or draw: all that matters for them is the Grand Slam and the world record 19th win.
They are looking more and more like the complete team and the most realistic rivals to the All Blacks in the game right now.
Before the Six Nations, Ireland had realistic claims of living in that elite company but they have fallen short of their own standards.
After naming his team on Thursday, Joe Schmidt said only the best possible performance will do to beat this England team who hit new heights of performance in the face of tepid resistance against Scotland last week.
The Ireland coach has repeatedly talked up England's depth this week and his point is enhanced by the fact that Conor Murray will not be wearing the No 9 shirt.
Andrew Conway will be the 20th player handed a debut by Schmidt since the 2015 World Cup if he comes off the bench today, but during that time no-one has emerged as a serious rival to the outstanding Munster No 9.
Luckily, Murray has never been unavailable for a Schmidt selection until today.
Only Jamie Heaslip has started more games than the 27-year-old, who is a major presence in the Irish defensive line, controls the pace of the game and takes pressure off Johnny Sexton.
Kieran Marmion has been consistently good for Connacht over the past three seasons, but his breaking style is suited to the province's running style.
"They're very different types of scrum-halves," Ireland skills and kicking coach Richie Murphy said earlier in the tournament.
"I think Kieran has still got a way to go in terms of how we try to play. He is a really good running scrum-half, a really big threat later on in the games. Where we're seeing him at the moment is that he could cause a lot of trouble when teams are starting to fatigue.
"Conor is probably a little more classic. He kicks well, passes well, he understands the game, he deals with the pressure very well and I still think he has a fair bit of an edge in relation to his passing and kicking game over Kieran at the moment."
The other big concern for Ireland is their lineout, where another Schmidt stalwart is absent from the starting XV, although Devin Toner will see some time off the bench.
After losing three key balls in Cardiff, it is a curious call to remove the totem of your set-piece and not introduce a jumping back-row, and it makes Rory Best's life all the more difficult as he faces an English pack containing three second-rows.
"You've just got to be smarter with where you go," the captain said. "There's no point trying to take them on head-on. We've got to be able to manipulate things and back each other.
"We felt when we looked back at the game last week there were our own errors that caused the three lineout losses.
"That's where you've got to be better and that's the 1pc we talk about that can make a massive difference at this level."
Ireland don't feel like they've been far away in their defeats, but their margin for error closes hugely this evening. England bring with them a formidable team to go with their winning record.
Up front, their tight five is the match of anyone's, while their back-row pack plenty of power on both sides of the ball.
Ben Youngs is a scrum-half who can thrive on front-foot ball, while George Ford and Owen Farrell are combining as part of the best passing 10-12 axis in European rugby. Outside them, there is blistering pace that will exploit any Irish narrowness.
How does Ireland's threat match up? Their tight five should hold their own in the scrum, whereas their lineout looks deficient. Their back-row lacks height and is in need of a big outing after being outplayed by the Wales combination, while Marmion and Johnny Sexton have never started together.
Their centres are excellent young players who are still growing together, while their back-three sees one class act replace another as Jared Payne comes in for Rob Kearney.
The New Zealander is an intriguing addition and if he can replicate his performances from the summer tour to South Africa, when he added a new attacking dimension from the No 15 jersey, he adds creativity in attack. Whether he can do it again in the white heat of Six Nations battle remains to be seen.
Much depends on the quality of ball Ireland's pack can provide to their backs, especially given England's form for disrupting at set-piece and dominating the collision zone.
As if it wasn't already a difficult task for Ireland, the addition of Billy Vunipola and Anthony Watson makes life even tougher.
The pair have always been difficult for Schmidt's side to handle, with the No 8 a force of nature with a sumptuous passing game and the Bath winger capable of taking most Irish defenders on the outside.
Facing up to his brilliant son, defence coach Andy Farrell has his work cut out. Ireland have struggled against teams playing with width and in that regard this will be a huge test.
Ireland's line-speed will be key; their ability to cut off clean supply to Youngs and preserve the gain-line will determine whether the English can get their game going; if they get momentum they will be difficult to stop.
With the Lions tour taking the best players for the summer, Schmidt's Ireland won't reconvene as a full-strength group until November. That's eight months to stew on a campaign that has failed to live up to its promise.
Beating England won't fix their disappointment, but it will ease the pain and pressure.
Unfortunately for Schmidt, the perfect performance has evaded his team to date and the loss of Murray makes it even more difficult to attain.
History is within the visitors' grasp and they've let nothing pass them by on Jones' watch yet.
Ireland stand in their way, but they have their own goals to focus on.
The bottom half of the table looms if they can't produce something special. That fear may not be enough against this quality English side.