Steve Hansen says the winner of New Zealand's Test match against Ireland in Dublin on Saturday will have the right to call themselves 'the best side in the world'.
The All Blacks are currently top of the world rankings, and travel to Dublin on the back of a win over England at Twickenham.
Ireland are the best of the rest, with New Zealander Joe Schmidt having led them to number two in the world after three Six Nations titles in the last five years.
But Hansen believes the Dublin Test, and not the rankings, will determine who is the world's greatest team, saying: "It is one and two, so whoever wins will be the best side in the world regardless of rankings.
"They are the number two side in the world and you don't get to play one and two that often when they are in two separate hemispheres, so when they do come about, they become pretty big games.
"That is the mental state people take out of it so it is going to be a good one."
The previous meeting between the two sides came two years ago in Ireland, and ended in an All Black victory.
However, the preceding Test took place in Chicago, and saw Ireland record a long-overdue first ever victory over New Zealand.
Hansen believes that victory, and Ireland's gradual improvement under Schmidt, has increased the stakes when the two sides meet.
"There is a fierce rivalry there and both packs will want to dominate," Hansen said. "Everyone seems to find another 10 percent when they play us because it is a good story if you can beat the All Blacks and everyone gets excited by that.
"So that will bring a lot more intensity to the game and I am picking it will be fast and the physical side of the game will be tough as will the mental side."