With champions France losing 24-18 to Wales in Paris on Saturday, and Eddie O'Sullivan's men claiming back-to-back Championship wins over the World champions, the Irish are now ranked as the leading side in the Northern Hemisphere.
O'Sullivan's charges have won ten games and lost three - since bowing out of the 2003 Rugby World Cup to France, 43-21.
The new IRB Rankings, released today, see France and Ireland swap places in fourth and fifth, less than a fortnight ahead of their Six Nations meeting in Dublin.
England and Wales remain in sixth and seventh, with Scotland's 18-10 win over Italy - coach Matt Williams' first Championship success since taking over last year - seeing them rise above Fiji, and into ninth.
NEW IRB WORLD RANKINGS: Released Monday, February 28:
(1) New Zealand 90.90 Ranking points(2) Australia 88.58