The eight teams are fighting for four places at next summer's World Cup in Russia.
The eight remaining European nations still fighting for a place at next summer's World Cup have inched closer to Russia after discovering who they will face in the UEFA playoff round next month.
With top spot in each qualifying group guaranteeing automatic passage to the final tournament, the eight best runners-up have one more chance to make it through - Slovakia were the second place team with the worst record and therefore missed out.
The draw was made in Zurich, Switzerland, with the four highest placed team on the latest FIFA World Rankings - Switzerland (11th), Italy (15th), Croatia (18th), Denmark (19th) - seeded.
Having leapfrogged Wales to finish second in their group and reach this stage, the Republic of Ireland, the lowest ranked team in the draw, will now face Denmark.
Four-time World Cup winners Italy must navigate a tricky tie against Sweden, while minnows Northern Ireland are to play Switzerland as they look to reach the final tournament for the first time since 1986.
2018 World Cup UEFA Playoff Draw:
Northern Ireland vs Switzerland
Croatia vs Greece
Denmark vs Republic of Ireland
Sweden vs Italy
Both legs of the playoff ties will take place between the 9th and 14th of November, with the team drawn first to play the first leg at home.