The two-legged ties will determine the four sides who will join Europe’s nine group winners - France, Portugal, Germany, Serbia, Poland, England, Spain, Belgium, and Iceland — at Russia 2018. The eight best second-placed teams (Slovakia missed out despite finishing runners-up to England in Group F) will battle for the four remaining qualifying spots. Joining Northern Ireland and the Republic of Ireland in the draw are: Sweden, Switzerland, Denmark, Italy, Greece, and Croatia.
The eight qualified teams have been divided into two pots based on the world rankings. Based on the rankings, Switzerland (11th), Italy (15th), Croatia (18th), and Denmark (19th) will be in pot one and will play one of the four teams in pot two. The second pot will contain Northern Ireland (23rd), Sweden (25th), Republic of Ireland (26th), and Greece (47th), so Northern Ireland and the Republic cannot play each other. Likewise they cannot play Sweden or Greece.
The Republic have won three of eight play-off ties, but two of those wins have come at the last two attempts, against Estonia to go to Euro 2012 and Bosnia-Herzegovina to advance to Euro 2016. Northern Ireland are new to the play-offs, having qualified automatically for last year’s European Championships.
Italy. The Azzurri are only in the play-offs because they had the misfortune of being in the same qualifying group as Spain. They may be lower than Switzerland in Fifa’s rankings, but they will still be a formidable opponent.
Home and away fixtures will be played between November 9 and November 15. The order of fixtures will be determined by the draw. Once one ball has been taken from pot one and another from pot two, they will be placed in a central pot, mixed and then drawn one by one. The first ball drawn will host the first leg between November 9 and 11. The return leg takes place between November 12 and 14.
The winner is decided on aggregate, so the scorer of the most goals advances to the World Cup finals. In event of a draw on aggregate, away goals apply. If there is still no deciding factor at the end of normal time, then the tie will go to extra time (two periods of 15 minutes), with the away goals rule still applicable. If there is still no winner, then the tie will go to a penalty shootout.