Champions Ireland retained their Six Nations title on points difference after an extraordinary final day.
The last round of games concluded with England falling agonisingly short of the 26-point winning margin they needed as they beat France 55-35 in an epic.
The day had started with Wales annihilating Italy 61-20 in Rome.
Ireland needed a huge win and their 40-10 demolition of Scotland was enough to both pass Wales and set a target just beyond England.
With three teams on three wins apiece going into the final round of games the stage was set, and what followed was one of the most incredible days in the tournament since it was first played in 1883, with 221 points scored in the three matches.
England started Saturday as leaders - just - from Ireland on points difference with Wales some way further back, and they would play in reverse order to decide who would become champions.
In the opener, Wales only led Italy by a point at half-time in Rome but cut loose in the second half, with George North's hat-trick ensuring Ireland needed to beat Scotland by 21 points to take the lead on points difference.
The champions duly hammered Scotland by 30 points in Edinburgh, meaning Wales were out of contention and that England needed to beat France by 26 points to take the title.
In a see-saw encounter at Twickenham, England pulled steadily clear but never managed to get into a lead that would have denied Ireland the title.
However, Jack Nowell's try with five minutes remaining put them 20 points ahead and meant a converted try would have given them the Championship.
They spent the closing moments hammering away at the French line in search of the winning points, and came within a foot of scoring, but in their desperation they infringed and the final whistle meant that although they had won handsomely, it was Ireland who are 2015 Six Nations champions.
How stunning Six Nations finale unfolded
- In first game Wales only lead 14-13 against Italy at half-time
- But seven second-half tries see them win 61-20 and go top
- Ireland need a 21-point win and lead Scotland 20-10 at the break
- Ireland go on to win 40-10, putting Wales out of the running
- England chase a 26-point win over France to take title
- France lead 15-7 after 18 minutes in a remarkable game
- England recover to win 55-35, but the trophy goes to Ireland
Reaction from the winners - and losers
Ireland captain Paul O'Connell: "I never would have predicted such a game at Twickenham. Fair play to England and fair play to France. I've never received a trophy in such a bizarre situation [after being handed the cup on the Murrayfield pitch]. It's strange. In some ways it's better than last year."
England head coach Stuart Lancaster: "I'm gutted really. It was one of the most courageous performances I've seen from a team. It was an unbelievable game of rugby."
Ireland head coach Joe Schmidt: "It was tumultuous. Exhausting. I spare a thought for England, they were superb today and probably deserved a share of the spoils."
England scrum-half Ben Youngs: "I don't really know what to say. I'm devastated. Congratulations to Ireland. We're devastated. We gave it a crack, but you can't let them get back in the game."
Ireland's two-try scorer Sean O'Brien: "We knew what we had to do at half-time and we executed it very well. It was important we expressed ourselves. We had to win the game first and foremost and we stuck to our guns and got the result."
Wales head coach Warren Gatland: "We knew if we scored a couple of tries to get ahead of Italy we would break their spirit. It was a great second-half performance."
Former England hooker Brian Moore: "England will feel desolate. There is very little to choose between the top three teams on any given day."
Former Scotland full-back Gavin Hastings: "I am massively, massively disappointed by Scotland. I expected them to come out and put on a performance. But they have laid down and that is very sad to see."