If Iceland gets past Croatia, it will become the smallest country in terms of population to reach the World Cup.
Trinidad and Tobago, with about 1.2 million inhabitants, is currently the least populous nation to qualify for the World Cup, in 2006. Iceland has close to 320,000 inhabitants.
The turnaround in Iceland's fortunes has been sparked by the appointment of coach Lars Lagerback in October 2010. At one stage, the team was ranked below Liechtenstein, but Lagerback's experience of guiding his native Sweden to two straight World Cups has quickly shone through and Iceland finished second in Group A behind Switzerland in 2014 qualifying.
Lagerback also led Nigeria at the 2010 World Cup in South Africa.
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TICKET FURY
Roughly 10 percent of Iceland's population tried to get tickets for the country's biggest ever football match. Only those up bright and early or extremely late got their hands on them.
Iceland football officials controversially put the tickets on sale at 4 a.m. local time at the end of last month, intending to avoid a website crash. They were sold within 3 hours, with many not even knowing they had even gone on sale.
Thore Shelly, Iceland's director of football, was forced to apologize for the way the ticketing process took place.
There will be about 10,000 fans at the Laugardalsvollur national stadium.
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WEATHER ISSUES
The Croatians won't just be taking on a fired-up host in Friday's first leg, they will also be battling testing weather conditions.
With diminishing daylight and dropping temperatures, Iceland's climate is very different from Croatia's and Friday's forecast doesn't look favorable.
The forecast is 0 degrees C (32 degrees F) with sleet and snow, and referee Alberto Unidiano Mallenco has arrived a day earlier than planned to determine whether the field is playable due to the weather.
The national stadium has never staged an international game so late in the year, so preparations started last week to get the field as game-ready as possible. A special fabric was placed over the grass with hot air blowing under the cloth to keep heat on the field until kickoff.
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KOVAC DEBUT
The match marks the coaching debut for Niko Kovac, who stepped up from Croatia's under-21 team after Igor Stimac was fired for failing to guide the team directly to the World Cup.
The Croatians finished second in Group A behind Belgium and are aiming for a return to football's biggest stage after missing out at the 2010 tournament.
"I can see a spark in the eyes of my players," Kovac said. "I can see they want to prove to the public that they are better than people think. They want to prove they are top players and a top team who deserve a ticket to Brazil.
"You will see the true face of the Croatian national team in this first match."
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CORRUPTION ALLEGATIONS
The build-up to the game has been overshadowed in Croatia by a TV documentary that looks at corruption and match-fixing in Croatian football.
It led to the head of the Croatian Football Federation, Davor Suker, kicking a Croatian state TV crew off the charter plane that took the players to Rejkjavik because he was angry about the documentary.
Indeed, there hasn't been much excitement in Croatia ahead of the playoffs, with fans believing it will be an easy job for the team over the two legs.
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Associated Press writers Jenna Gottlieb and Dusan Stajanovic contributed to this report.