The final four sides to make it to Euro 2012 in Poland and Ukraine will be decided over two legs on November 11 and November 15.
The winners will come up against the likes of Spain, the Netherlands and Germany, the top three sides in the world, according to FIFA's rankings.
Some of the world's biggest names will be in action during the play-offs: Cristiano Ronaldo, Nani, Petr Cech, Luka Modric, Robbie Keane and Edin Dzeko. All will be fighting it out for the chance to represent their country next summer.
Some of these teams have history against each other, and others have experienced the best and worst of what the play-offs have to offer; Ireland's heartbreaking defeat against France in World Cup 2010 qualifying is still fresh in Irish minds.
So, here is all the latest team news in the build-up to the first leg, as well as my predictions for who will qualify for the competition.
Portugal boast a squad with the likes of Cristiano Ronaldo and Nani, but they failed to qualify through the group stage and must now travel to the Balkans to face a Bosnia-Herzegovina side that very nearly edged out France to qualify from their group.
Portugal will have been disappointed not to have qualified from their group, a shocking 4-4 draw against Cyprus proving to be a particularly low point for a side that just last year beat world and European champions Spain.
Portugal, managed by Paulo Bento, have left Jose Bosingwa out of their squad, and, according to Goal.com, will be without the Chelsea defender for some time to come; he has ruled himself out of the side while Bento is manager.
Ricardo Carvalho walked out on the squad before the qualifier against Cyprus earlier this year and has announced his retirement from international football, leaving Portugal without one of Europe's top defenders.
The Portuguese will also be without midfielder player Danny and right-back Silvio, according to a report from Goal.com.
Bosnia-Herzegovina should not be underestimated. In Edin Dzeko, they have a striker in superlative form who is used to playing against the best Europe has to offer.
Asmir Begovic has put in some good displays for Stoke this season and has gained valuable European experience with the Premier League side.
Portugal are undoubtedly favourites; Ronaldo and Nani give Portugal the creative edge and with the likes of Pepe and Fabio Coentrao, they have some of Europe's top players.
Bosnia-Herzegovina are yet to qualify for a major tournament, but the men from the Balkans are used to punching above their weight; Portugal have a fight on their hands.
In the end, I believe Portugal will win out, despite the damaging effects of the infighting with manager Paulo Bento.
Predicted score over both legs: Portugal 4-3 Bosnia-Herzegovina.
Ireland's last play-off experience, against France, was controversial to say the least. Thierry Henry's handball led to an international outcry, something Ireland would rather avoid on this occasion.
Ireland have some major injury problems heading into the first leg of the play-off, to be played in Tallinn, Estonia. John O'Shea is out after picking up an injury against Aston Villa, Shane Long is out for six weeks with a knee injury also sustained against Aston Villa, and Darren Gibson could miss out due to a foot injury (all courtesy of BBC Sport).
According to the Independent, Leon Best will miss the first leg of the tie; he is expecting the birth of his first child. Shay Given didn't take part in training earlier this week, but is not considered a doubt, according to a report from The Press Association, and Kevin Doyle is suspended after being sent-off in Ireland's last qualifier (BBC Sport).
Despite all those injury problems, Ireland still have a great chance of making it to their first major tournament since the 2002 World Cup.
Ireland still boast a squad with plenty of Premier League experience and in Robbie Keane, they have a proven goalscorer.
Estonia went on an incredible run during the final stages of European qualification; they beat both Slovenia and Serbia to secure a play-off spot.
Konstantin Vassiljev could be a major threat to Irish hopes. The Estonian pulled his country back from the brink of elimination with two goals against Northern Ireland, including the stunning strike in the video above.
Estonia have the best side they have ever had. They will still need to play out of their skins if they are to see off Ireland, especially considering the second leg is to be played in Dublin, although Ireland's goalscoring potential has been reduced somewhat through injury and suspension.
Predicted score over both legs: Estonia 1:3 Ireland.
The teams that finished behind Spain and England in the group round will meet, with a place at Euro 2012 on the line.
Montenegro held England to two draws in qualifying, coming from two goals down when the teams met in Podgorica, but losses against Switzerland and Wales and a draw with Bulgaria meant they only just made it into the play-offs.
Montenegro will welcome back Branko Boskovic, of D.C United, but Marko Basa is out with a shoulder problem (both courtesy of Yahoo). Aside from those two alterations, Montenegro should remain unchanged.
Mirko Vucinic, Montenegro's captain, is probably his side's biggest threat to Czech hopes, as the nation that split from Serbia in 2006 look to qualify for their first major international competition.
The Czech Republic will be favourites going into the first leg of the play-off. Petr Cech is a doubt after suffering a broken nose, but he has had a mask made so that he can play, according to ESPN. Even if the mask fits, he could still miss out on the first leg of the tie.
In Tomas Rosicky and Milan Baros, the Czech Republic have two players used to playing at the top level of European club football and will be used to this type of do-or-die situation.
Both sides were solid defensively during qualifying; Montenegro conceded seven goals and the Czech Republic, eight. Montenegro struggled for goals, notching up just seven, while the Czech side managed 12.
The Czech Republic should see off the Montenegrin threat, although their comeback against England shows that they will not go down without a fight.
Predicted score line over both legs: Czech Republic 3:1 Montenegro.
A rematch of Euro 2008's quarterfinal gives Croatia a shot at revenge, and they will be confident of reversing their fortunes against a Turkish side that has not had an easy time of it in qualifying.
When results against the bottom side of each of the groups with six sides are removed (some groups had five sides, others six), Turkey have the worst record of any team in the play-offs. They finished just two points clear of Belgium and won only once away from home.
They will also be without the services of Nuri Sahin, who has only just returned from a lengthy lay-off (Fifa.com). They can still, however, rely on the services of the Altintop brothers.
In Guus Hiddink, the Turks have a manager who knows how to spring surprises on the international scene. He took South Korea to a World Cup semifinal in 2002 and Russia to the Euro 2008 semifinals. In short, the Turkish side should not be taken lightly.
Croatia have injury problems of their own. Mladen Petric, Ivan Strinic, Niko Kranjcar and Dejan Lovren are all injured (Fifa.com).
Although, they do have Nikica Jelavic and Luka Modric in top form.
Croatia should have won their group, and the added incentive of revenge after Euro 2008's heartbreaking penalty shoot-out loss, in conjunction with a side which, on paper, looks better than Turkey's and should be enough to see the Croatian men through.
The Turks will certainly give their all, and the Hiddink factor should not be underestimated, but Croatia have to be favourites to qualify, especially with the second leg to be played at home.
Predicted score line over both legs: Croatia 3:0 Turkey.