Ireland, England and France all head into Saturday's final round of rugby's Six Nations matches with a chance of winning the title.
The three teams are level at the top of the standings on six points after each recording three wins from four matches.
The Irish are in pole position as they have a cumulative points difference of +81 and a points difference advantage of +49 over second-placed England.
Points difference is the initial tie-breaker if teams are level on tournament match points.
Ireland play France in the final match of the Championship - Saturday's kick-off times have been staggered to ensure the largest possible television audience despite criticism this creates an unfair advantage for the two sides playing last.
Realistically, any sort of Ireland win is likely to give them the title, but defeat or a draw - the result of their past two matches against France - could see them pipped at the post should England beat Italy in Rome.
The Irish have the added incentive of sending retiring icon Brian O'Driscoll out in style.
O'Driscoll, who will bow out with a world record 141 caps (including eight for the British and Irish Lions), will have struck fear into the French after his scintillating display in the crushing 46-7 win over Italy last Saturday, creating three tries.
"I feel we have the capabilities now of winning in Paris of course, more so now than other times we've gone over there," said O'Driscoll.
"But I realise how tough a challenge it is - we've won once there in 42 years, it's one win, and one draw in 42.
"We realise the size of the challenge, but we feel when we go well, we're difficult to contain, so we have to get ourselves up for one massive performance."
England are in the trickiest position of all three contenders given, as their match against Italy in Rome is the first of the day.
The first order of business for England is to maintain their perfect winning record against Italy as a shock loss would scupper their title hopes, with either France and or Ireland guaranteed to add their tournament points tally.
England currently have a +29 points difference advantage over third-placed France.
If England beat Italy, a subsequent narrow French win could see them take the title after two successive runners-up finishes in coach Stuart Lancaster's two previous Six Nations in charge.
Equally, an England win in Rome allied to a draw in Paris would see Lancaster's men lift the trophy.
France must beat Ireland as a draw won't be enough to finish on top, regardless of what happens to England in Rome.
If England lose, just beating Ireland will be enough to give France the title.
However should England, as widely expected, defeat Italy, then France will need to beat Ireland and beat them well to take the title on points difference.
France haven't lost to Ireland in France since 2000 and their previous defeat by the Irish on home soil was back in 1972.